LOANED   TO 
UNIVERSITY   OF    CALIFORNIA 

DEPARTMENT    OF     MECHANICAL     AND     ELECTRICAL     ENGINEERING 
FROM     PRIVATE    LIBRARY    OF 

C.    L.    CORY 
1930 


DESIGNS    FOR    SMALL 
DYNAMOS    AND    MOTORS 


BY 

CECIL  P.  POOLE 

MEMBER   OF   AMERICAN    INSTITUTE   &F   ELECTRICAL   ENGINEERS 


i 


NEW  YORK 

McGRAW  PUBLISHING  COMPANY 
1906 


Engineering 
Library 


ft 


Engineering 

I  -Vary 


COPYRIGHTED  1906 

by  the 
McGRAW  PUBLISHING  COMPANY,  NEW  YORK 


PREFACE 

MOST  of  the  chapters  of  this  book  originally  formed  articles  written  for 
the  American  Electrician,  and  many  of  them  were  published  in  the  book 
entitled  "  Electrical  Designs."  Chapters  X  to  XVIII  inclusive,  however, 
have  not  previously  appeared  in  book  form,  and  all  of  the  direct- current 
designs  herein  described  have  been  revised  in  accordance  with  the  changes 
in  the  practice  of  dynamo  and  motor  design  which  have  occurred  since 
their  first  publication. 

The  majority  of  the  designs  were  prepared  with  a  view  of  reducing  to 
the  simplest  degree  the  facilities  necessary  for  the  construction  of  the 
machines,  rather  than  to  secure  the  most  graceful  outlines  or  best  efficiency. 

Chapters  XIX  to  XXII  inclusive  describe  designs  by  Mr.  J.  C.  Brock- 
smith  which  were  previously  described  in  issues  of  the  American  Electrician 
that  are  now  out  of  print.  These  were  also  reprinted  in  ''Electrical 
Designs,"  which  is  superseded  by  the  present  book  and  three  others  now 
in  press.  The  other  volumes  are  devoted,  one  to  electrical  instruments, 
telephones  and  similar  light  constructions,  another  to  heavier  electrical 
apparatus  other  than  dynamos  and  stationary  motors,  and  the  third  to 
gas  engines  and  other  machinery  not  involving  electrical  construction. 
These  volumes  will  contain  all  of  the  material  that  appeared  in  "Electrical 
Designs,"  excepting  that  contained  by  the  present  book,  together  with 
much  additional  matter  not  heretofore  printed  in  book  form. 

C.  P.  P. 

NEW  YORK,  December  i,  1905. 


789547 


CONTENTS 

CHAPTER  PAGE 

I.    ONE -SIXTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE     ...  i 

II.    ONE-SIXTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE        ...  8 

III.  ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE    ...  14 

IV.  ONE -FOURTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE     ...  22 
V.    ONE -HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE        ...  29 

VI.     ONE  HORSE-POWER  BIPOLAR  MOTOR  WITH  DRUM  ARMATURE        .     .  41 

VII.    ONE  HORSE-POWER  FOUR-POLAR  MOTOR  WITH  DRUM  ARMATURE       .  53 
VIII.    Two  HORSE-POWER   FOUR-POLAR   MOTOR   WITH   TWO-PATH   DRUM 

ARMATURE 65 

IX.    THREE  HORSE-POWER  MOTOR 76 

X.    DIRECT-CURRENT  IIO-VOLT  FAN  MOTOR         84 

XI.    THREE  HORSE-POWER  LAUNCH  MOTOR 90 

XII.    MULTIPOLAR  THIRTY-FIVE -LIGHT  INCANDESCENT  DYNAMO       ...  97 

XIII.  SEVENTY-FlVE-LlGHT  INCANDESCENT  DYNAMO 10$ 

XIV.  FOUR-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 112 

XV.    A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO    .....  114 
XVI.    SELF-STARTING    SINGLE-PHASE    INDUCTION    MOTOR   OF    ONE-HALF 

HORSE-POWER      .           ,     . 124 

XVII.    ONE  HORSE-POWER  SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR  132 

XVIII.    Two  HORSE-POWER  SELF-STARTING  SINGLE -PHASE  INDUCTION  MOTOR  141 
XIX.    ONE-KILOWATT    COMBINED    ALTERNATING    AND    DIRECT-CURRENT 

MACHINE .     .     .     .     .     .     .    •.     .     .     .  149 

XX.    TWO-KILOWATT    COMBINED    ALTERNATING    AND    DIRECT-CURRENT 

MACHINE 162 

XXI.      FOUR-KILOWATT      COMBINED     ALTERNATING     AND      DIRECT-CURRENT 

MACHINE      .     .     .     .     ...     »     . 169 

SINGLE -PHASE  RECTIFIER .     .     .     .     .     .     .  178 


DESIGNS    FOR   SMALL    DYNAMOS    AND 

MOTORS 


CHAPTER  I 
ONE-SIXTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 

IN  preparing  this  design  and  those  which  follow,  it  has  been  assumed 
that  any  one  who  is  sufficiently  interested  in  the  subject  to  undertake  the 
construction  of  a  motor  or  dynamo  will  be  sufficiently  familiar  with  electro- 
mechanics  to  exercise  individual  judgment  in  the  matter  of  fitting  the 
various  parts,  and  also  in  the  design  and  construction  of  brush  holders, 
terminal  blocks,  and  such  other  parts  as  are  not  of  controlling  importance 
in  the  electrical  design  of  the  machines.  Detailed  descriptions  of  these 
parts  will,  therefore,  not  be  given;  the  reader  may  easily  inform  himself 
concerning  these,  if  necessary,  by  inspecting  a  finished  machine  of  almost 
any  type,  or  by  reference  to  any  good  text-book. 


FIG.  i 

The  accompanying  sketches  are  intended  to  serve  as  working  drawings 
in  the  construction  of  a  J  horse-power  motor,  for  operation  upon  a  i  lo-volt 
direct-current  circuit.  In  Figs,  i  and  2,  M  is  the  field  magnet,  consisting 

i 


FOR  SMALL  DYNAMOS  AND  MOTORS 


of  a  bar  of  wrought  iron  or  mild  steel  3  ins.  wide  and  ij  ins.  thick,  bent 
into  the  shape  shown;  the  inner  surface  of  each  limb  is  machined  smooth 
a  distance  of  three  inches,  forming  shallow  mortises  to  receive  the  pole- 
pieces,  P  P,  which  are  secured  by  J-in.  cap  screws  passing  through  the 
magnet  limbs.  The  pole-pieces,  P  P,  are  of  gray  cast  iron,  and  should 
be  finished  on  all  sides  to  remove  the  scale  as  well  as  to  improve  the  ap- 
pearance of  the  completed  machine.  The  magnet,  M,  might  be  made  to 
look  neater  by  touching  up  its  sides  on  a  coarse  emery  wheel;  it  should 
be  well  annealed  after  bending  and  finishing. 

Two  holes,  h,  h,  are  bored  through  the  pole-pieces,  after  these  are 
fitted  to  the  magnet,  but  before  the  armature  chamber  is  bored  out.  These 
holes  are  17-64  in.  diameter,  and  they  must  be  3!  ins.  apart,  center  to 
center,  and  equidistant  from  the  center  of  the  armature  chamber;  if  the 
magnet  limbs  conform  strictly  to  the  measurement  given  from  face  to 
face  of  the  finished  part  of  the  limbs,  the  centers  of  the  holes,  h,  h,  will 
each  be  3-16  in.  from  the  joint  between  the  magnet  and  the  pole-pieces. 
In  these  holes  are  to  be  inserted  J-in.  iron  or  steel  rods  7  J  ins.  long,  threaded 
at  each  end  a  distance  of  f  in.  Fig.  2,  which  gives  a  plan  view  of  the 


(D 


C) 


O 


o 


o 


p. 


FIG.  2 


magnet  and  the  journal  yokes,  F,  F,  shows  the  function  of  these  rods; 
they  support  the  yokes  and  carry  distance-pieces,  c,  c,  d,  d,  made  of  brass 
tubing  just  large  enough  to  slip  over  the  rods,  and  having  J-in.  walls. 
The  pieces,  c,  c,  are  if  ins.  long,  and  d,  d,  are  2\  ins.  long.  The  yokes 
are  held  in  place  by  brass  nuts,  not  shown  in  Fig.  2. 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE          3 

-;  The  journal  yokes,  F,  F,  are  alike.  They  are  of  cast  brass,  J  in. 
thick,  with  a  stiffening  rib  |  in.  thick,  on  each  side  of  the  journal  box. 
The  inner  endfc)f  one  box  should  be  trued  up  to  receive  the  brush  arm  or 
quadrant.  The  yokes  may  be  much  more  easily  and  accurately  fitted  if  a 
steel  template  is  used.  This  may  be  cheaply  provided  by  taking  a  piece 
of  flat  steel,  i  in.  wide  and  4^  ins.  long,  scribing  a  straight  line  approxi- 
mately down  the  center,  and  drilling  three  holes  as  shown  by  T;  Fig.  2, 
the  center  one  11-16  in.  and  the  others  J  in.  in  diameter.  After  the  box 
is  bored,  mount  it  on  a  mandrel  and  turn  down  the  inner  end  to  fit  the 
center  hole  in  the  template  T,  and  at  the  same  time  face  up  the  ends  of 
the  yoke  where  they  are  to  touch  the  distance-pieces;  put  the  template  on 
the  end  of  the  box  and  scribe  the  positions  of  the  J-in.  holes  on  the  ends 
of  the  yoke.  This  template  should  also  be  used  to  fix  the  distance  apart 
of  the  holes,  h,  h  (Fig.  i).  The  boxes  are  bored  out  9-16  in.  in  diameter 
and  fitted  with  bushings  of  J  in.  bore  and  i  in.  long;  oil  grooves  should 
be  cut  at  each  end  of  the  box  and  provision  made  for  taking  out  the  oil. 
Oil  cups  may  be  used  to  feed  the  bearings. 

After  the  yokes  are  fitted  the  frame  may  be  centered  in  a  lathe  as 
follows,  for  boring  out  the  pole-pieces.  Take  a  piece  of  f-in.  round 
machinery  steel  i.i  ins.  long,  and  make  the  shaft  5  (Fig.  3);  the  distance 
from  e  to  g  is  3^  ins.  and  the  diameter  there  is  f  in.;  from  g  to  i  is  3  11-16 
ins.  and  the  diameter  J  in.;  from  i  to  j  is  i  1-16  ins.  and  the  diameter 
f  in.;  from  j  to  k  is  3  ins.,  and  the  diameter  is  f  in.  Turn  the  ends  of  the 
shaft  down  to  a  point,  like  that  of  a  lathe  center;  put  it  in  the  boxes,  bolt 
the  yokes  in  place,  and  then  put  the  frame  on  the  lathe  carriage,  adjusting 
it  until  the  sharp  ends  of  the  shaft  are  in  exact  line  with  the  lathe  centers. 
Bolt  the  motor  down  in  this  position,  remove  the  yokes  and  shaft,  and  bore 
out  the  pole-pieces.  The  ends  of  the  shaft  should  afterwards  be  squared 
off,  care  being  taken  to  cut  exactly  J  in.  off  each  end,  leaving  the  shaft 
10  ins.  long. 

The  armature  (Fig.  3)  is  built  up  of  iron  discs  3  ins.  in  diameter  and 
not  more  than  1-32  in.  thick;  there  are  twelve  slots,  each  3-16  in.  wide 
and  f  in.  deep.  These  may  be  punched  in  each  disc  separately,  if  a 
stamping  press  is  available,  or  they  may  be  milled  after  the  discs  are 
assembled  on  the  shaft.  If  the  slots  are  milled  the  discs  should  be  taken 
off  the  shaft  afterwards  and  the  burrs  dressed  off,  care  being  taken  to 
reassemble  them  exactly  as  they  were  when  the  slots  were  milled;  this  may 
be  accomplished  by  taking  a  very  slight  cut  with  a  metal  saw  along  the 
top  of  one  tooth,  using  the  mark  as  a  guide  to  get  the  proper  slots  together. 
In  order  to  get  them  in  exact  alignment,  a  rectangular  bar  of  metal  should 
be  made  to  fit  snugly  in  one  slot  before  taking  the  discs  off;  when  they 
are  put  back  this  bar  is  inserted  in  the  slot  to  which  it  was  fitted  and  the 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


nut  is  set  up  hard.  End  plates,  W  W,  of  brass,  2  ins.  in  diameter  and 
3-16  in.  thick,  serve  to  prevent  the  end  discs  from  buckling  when  they  are 
compressed.  A  nut  (not  shown),  fitted  to  the  thread  which  begins  at  g  on 
the  shaft,  serves  to  clamp  the  discs,  which  are  held  at  the  other  end  by  the 
shoulder,  i  ;  no  key  is  necessary  to  prevent  the  discs  from  turning  on  the 
shaft  in  so  small  a  machine,  but  it  is  essential  that  they  should  be  clamped 
as  tightly  as  a  fairly  strong  man  can  clamp  them,  using  a  six-inch  wrench 
on  the  nut.  The  shaft  may  be  held  in  a  pipe  vise  between  i  and  /  when 
setting  up  the  nut;  the  nut  should  be  made  of  very  hard  bronze  metal  in 
preference  to  steel,  as  the  latter  attracts  magnetic  lines  of  force  and  is 
liable  to  heat. 

The  commutator  may  be  made  as  shown  in  the  sketch,  or  according 
to  any  other  modern  plan,  a  number  of  which  were  described  in  the 


t 

s 

p 

9 

FIG.  3 

American  Electrician  for  July,  1896.  The  only  essential  features  are  the 
space  along  the  shaft  which  must  not  exceed  f  in.,  the  width  of  face, 
which  should  not  be  less  than  \  in.,  and  the  number  of  segments,  which 
must  be  24.  The  commutator  here  shown  is  intended  to  be  secured  to 
the  shaft  by  a  small  steel  set-screw  through  the  hub  or  boss  at  the  front; 
the  end  of  this  hub,  /,  must  be  i  J  ins.  from  the  end  of  the  shaft.  Extreme 
care  must  be  taken  to  insulate  the  segments  from  the  shell  as  well  as  from 
each  other;  mica  is  the  only  reliable  material  for  this  purpose.  Carbon 
brushes  \  in.  wide  and  J  in.  thick  should  be  used. 

The  armature  core  is  next  prepared  for  winding.  Cut  four  discs  of 
heavy  drilling  (so-called  twilled  muslin),  2\  ins.  in  diameter,  with  a  f-in. 
hole  in  the  center;  varnish  the  ends  of  the  armature  core  with  shellac  and 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 


5 


varnish  two  of  the  cloth  discs,  each  on  one  side;  thread  them  on  the  shaft, 
one  at  each  end,  with  the  varnished  sides  next  to  the  core,  and  press  them 
tightly  on  the  core.  While  the  varnish  is  hardening  cut  24  pieces  of 
drilling  the  shape  of  t  (Fig.  3);  cut  two  slits  \  in.  long  in  each  end,  9-16  in. 
from  each  side,  and  3-16  in.  from  each  other;  varnish  the  strips  on  one  side, 
and  when  nearly  dry  bend  them  along  the  dotted  lines  so  as  to  form  troughs, 
with  the  varnish  inside  the  trough.  Varnish  the  outside  of  each  trough 
and  the  walls  of  the  slots  in  the  core;  put  two  troughs  in  each  slot  and 
turn  the  flaps,  u,  v,  w,  flat  against  the  end  of  the  core,  applying  enough 
fresh  shellac  to  hold  them  down.  Then  put  on  the  two  remaining  end 
discs  of  cloth,  first  varnishing  the  sides  next  to  the  armature;  after  they 
are  in  place  varnish  the  outsides  and  put  the  core  in  an  oven  to  bake, 
being  careful  that  the  oven  is  not  hot  enough  to  scorch  the  cloth.  A 
temperature  of  130  degs.  Fah.  is  sufficient.  After  baking,  tape  the  shaft 


Une 


FIG  4 


thoroughly  from  i  to  j,  and  from  the  other  end  of  the  core  to  where  the 
commutator  will  come. 

The  coils  consist  each  of  20  turns  of  No.  24  double-silk-covered  wire, 
wound  5  turns  wide  and  4  deep  in  the  slots,  but  spread  out  as  flat  as  pos- 
sible across  the  heads.  Wind  coil  No.  i  in  slots,  A  A'-,  coil  No.  2  in  B  B'; 
No.  3  in  C  C'\  No.  4  in  D  D' \  No.  5  in  E  E'rand  No.  6  in  F  P.  Coil 
No.  7  goes  in  A '  A,  on  top  of  coil  No.  i,  but  beginning  on  the  opposite 
side  of  the  core,  as  indicated  by  the  lettering;  No.  8  in  B'  B]  No.  9  in 
C'  C;  No.  10  in  D'  D-  No.  n  in  E'  E,  and  No.  12  in  F'  F.  Coils  13  to  24 
are  wound  on  top  of  the  first  12  coils  in  exactly  the  same  order.  After 
winding  each  coil  bring  the  finishing  end  across  to  the  slot  where  the  starting 
end  enters  and  twist  the  two  lightly  together.  When  all  the  coils  are  on 


6  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

untwist  the  coil  ends  and  twist  the  last  end  of  each  coil  to  the  starting 
end  of  the  coil  in  the  slot  next  to  it  on  the  right ;  these  twisted  ends  go  each 
to  a  commutator  segment,  in  regular  order. 


FIG.  6 

The  field  magnet  is  easily  made  ready  to  wind  by  taping  the  horizontal 
part  of  the  magnet,  two  layers  deep,  with  varnished  muslin  and  putting 
on  two  fiber  heads.  One  of  these  heads  is  shown  by  H  (Fig.  4).  It  is 
in  two  pieces,  the  seams  being  at  the  ends,  and  is  cut  from  J-in.  sheet 
fiber.  The  two  halves  may  be  clamped  together  on  the  core  by  means 
of  a  small  brass  wire  drawn  around  the  outer  edge,  laying  in  a  shallow 
groove,  the  ends  being  twisted  and  cut  close.  The  pole  pieces  should  be 
removed  before  taping  and  putting  on  the  heads,  to  facilitate  these  opera- 
tions as  well  as  the  winding  of  the  coil.  One  fiber  head  has  a  notch,  n, 
half  way  of  its  inner  long  side,  to  enter  the  field  wire.  The  coil  consists 
of  No.  28  single- cotton- covered  wire,  B.  &  S.  gage,  f  in.  deep  and  the 
full  length  of  the  available  space.  At  least  9,500  turns  should  be  got  on. 
The  field  winding  is  connected  in  shunt  to  the  brushes,  and  it  would  be 
a  good  plan  to  provide  a  starting  switch  and  resistance  lamp  connected 
up  as  shown  diagrammatically  by  Fig.  5,  where  F  is  the  field  coil,  B  B 
the  brushes,  L  a  32-candle-power,  loo-volt  incandescent  lamp,  S  the 
starting  switch,  m  a  magnet,  and  S  W  a  double-pole  snap  switch.  This 
arrangement  could  be  mounted  on  the  base  of  the  motor.  Fig.  6  shows 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE          7 

the  complete  motor  on  a  wooden  base,  Q,  without  the  pulley;  the  latter 
may  be  any  diameter  between  ij  ins.  and  2j  ins.,  with  a  i-in.  crown  face 
or  J-in.  grooved  face.  The  motor  is  secured  to  the  base  by  flat-head 
machine  screws  from  below,  entering  the  ends  of  the  wrought  iron  and 
countersunk  in  the  under  side  of  the  wood.  This  machine  will  stand  a 
momentary  overload  of  100  per  cent,  and  will  work  up  to  J  horse-power 
for  half  an  hour  at  a  time. 

WINDINGS    FOR   BATTERY   SERVICE 

In  order  to  adapt  this  motor  for  use  in  connection  with  a  battery  the 
following  windings,  etc.,  must  be  substituted  for  those  specified  above: 
The  armature  to  be  wound  with  six  coils  of  No.  12  wire,  each  having 
twelve  turns  (three  wide  and  four  deep  in  a  slot).  The  field  wire  will  be 
No.  19,  wound  17  layers  deep  and  83  turns  in  length.  The  commutator 
will  have  six  segments,  and  should  have  a  brush  surface  f  in.  wide;  copper 
brushes  f  x  J  in.  should  be  used,  the  contact  faces  being  cut  to  such  a 
bevel  as  to  present  an  area  of  J  in.  square  at  least.  Connect  the  field 
winding  in  shunt  with  the  armature,  instead  of  in  series  as  is  usually 
done.  This  winding  is  for  6  volts.  The  machine  thus  wound  will  stand 
an  armature  current  of  20  to  25  amperes. 


CHAPTER  II 
ONE-SIXTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE 

IN  Figs.  7  and  8  M  is  a  wrought-iron  magnet  core,  P  P  cast-iron  pole- 
pieces,  C  the  armature  core,  and  Y  the  journal  yoke.  The  magnet  core, 
M,  is  made  from  a  i  in.  x  4^  in.  bar  of  commercial  wrought  iron  bent 
to  the  shape  shown.  The  faces  of  the  arms  are  machined  to  a  depth  of 
1-16  in.,  where  the  pole-pieces,  P  P,  are  attached,  so  as  to  form  a  magnetic 
joint  of  as  low  reluctance  as  possible.  The  pole-pieces  are  secured  to  the 
magnet  arms  by  J-in.  cap  screws  passing  through  smooth  holes  in  the 
arms  and  tapped  into  the  pole-pieces;  the  latter  are  of  gray  cast  iron,  and 
should  be  finished  on  all  sides  sufficiently  to  remove  the  scale.  The 
magnet,  M,  might  be  improved  in  appearance  by  touching  up  its  sides 
with  a  coarse  emery  wheel ;  it  should  be  thoroughly  annealed  after  bending 
and  finishing.  It  will  be  noticed  by  reference  to  Fig.  8  that  the  ends  of 
the  magnet  arms  project  slightly  beyond  the  outer  faces  of  the  pole-pieces; 
this  is  done  in  order  to  furnish  a  guide  for  the  flanges  of  the  journal  yoke 
arms.  After  fitting  the  pole-pieces  to  the  magnet  arms  the  complete 
magnet  frame  is  bolted  to  the  lathe  carriage  in  position  for  boring  out  the 
pole-pieces;  before  this  is  done  it  is  necessary  to  drill  a  hole  through  the 
back  of  the  magnet  to  allow  the  boring  bar  to  pass  through,  and  also  to 
form  a  seat  for  the  rear  bearing.  This  hole  is  i  in.  in  diameter,  and  the 
magnet  frame  must  not  be  allowed  to  move  from  its  original  position  on 
the  lathe  carriage  from  the  time  the  hole  is  drilled  until  all  the  circular 
tooling  on  it  is  accomplished. 

After  drilling  the  hole  in  the  back  of  the  magnet  adjust  the  boring 
bar  and  bore  the  armature  chamber  out,  4  11-16  ins.  in  diameter.  Next 
adjust  the  boring  tool  so  that  it  will  scribe  on  the  ends  of  the  magnet  arms 
arcs  of  a  circle  6  ins.  in  diameter;  then  cut  away  the  wrought  iron  inside 
the  scribed  marks,  down  flush  with  the  pole-pieces,  as  shown  in  Fig.  7, 
forming  recesses  for  the  flanges  of  the  journal  yoke.  The  yoke  and  box 
are  cast  in  one  piece  of  brass  or  other  non-magnetic  composition;  the 
shell  of  the  box  is  ij  ins.  long,  and  projects  J  in.  beyond  the  inner  face 
of  the  yoke;  the  outer  diameter  of  the  shell  is  i  in.,  and  it  is  bored  out  to 

8 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE  9 

f  in.  inner  diameter  and  bushed  to  f  in.  The  yoke  and  arm  portions  are 
3-16  in.  thick,  with  a  J-in.  stiffening  rib  on  each  side  of  the  box,  and  the 
arms  taper  from  i  in.  wide  at  the  flanges  to  about  J  in.  near  the  box.  The 
flanges  are  2  ins.  long,  f  in.  wide,  and  \  in.  thick  after  facing;  the  arms, 
beyond  the  bends,  are  sufficiently  long  to  make  the  distance  from  the  face 
of  the  pole-piece  to  the  inner  face  of  the  yoke  2  ins.  After  boring  the  box 
it  is  mounted  on  a  stiff  mandrel  and  the  surfaces  of  the  flanges  that  go 
next  the  magnet  are  faced  up  true ;  next,  the  outer  edges  of  the  flanges  are 
skimmed  off  until  the  yoke  fits  snugly  between  the  curved  edges  of  the 
recesses  previously  cut  in  the  ends  of  the  wrought-iron  magnet.  Care 
must  be  taken  in  making  the  pattern  for  the  yoke  that  the  inner  edges 
will  not  project  inward  beyond  the  bore  of  the  pole-pieces.  The  yoke  is 
fastened  to  the  pole-pieces  by  screws,  as  indicated  in  Fig.  7. 


FIG.  7 

The  rear  bearing,  7,  is  a  little  peculiar  in  construction.  The  box  portion 
is  similar  to  that  part  of  the  yoke,  but  it  is  cast  with  a  flange,  /,  i  in.  from 
the  farthest  end  of  the  shell,  which  is  ij  ins.  long.  A  collar,  n,  is  fitted  to 
screw  onto  the  outer  end  of  the  shell,  which  is  threaded  for  that  purpose. 
The  shell  is  turned  down  outside  to  fit  snugly  in  the  hole  drilled  in  the 
back  of  the  magnet,  and  when  it  is  inserted  in  the  hole  the  collar,  n,  is  put 
on  and  screwed  up  tight.  This  box,  like  the  front  one,  is  bushed  to  f -in. 
bore.  The  drawing  shows  the  flange,  /,  and  collar,  n,  countersunk  in  the 
metal  of  the  magnet;  this  will  not  be  necessary  if  the  magnet  is  smoothed 
up  with  an  emery  wheel,  as  above  suggested,  the  object  in  countersinking 
being  to  provide  smooth,  true  bearing  surfaces  for  the  flange  and  collar. 


IO 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


The  armature  core,  spider,  and  shaft  are  shown,  partly  in  crossrsection, 
by  Fig.  9.  The  core  is  built  up  of  low  carbon  steel  rings,  4j  ins.  outside 
diameter  and  2\  ins.  inside,  not  more  than  1-32  in.  thick;  these  are  assem- 
bled on  a  brass  drum,  shown  by  Fig.  n,  which  should  be  2§  ins.  outside 
diameter  before  finishing,  so  that  it  may  be  turned  down  to  exactly  fit  the 
inner  circle  of  the  armature  rings;  the  wall  of  the  drum  is  \  in.  thick  after 
finishing,  and  there  are  four  equidistant  projecting  lugs,  /,  J  in.  long,  on 
each  end,  by  which  the  drum  is  secured  to  the  spider  (see  Figs.  9  and  10). 
The  rings  forming  the  core,  C  (Fig.  9),  are  compressed  and  held  on  the 
drum,  r,  by  two  brass  washers,  w,  w,  3-16  in.  thick  and  3!  ins.  outer  diam- 
eter, which  screw  onto  the  ends  of  the  drum.  The  core,  when  compressed, 
is  ij  ins.  long,  and  has  24  slots  3-16  in.  wide  and  7-16  in.  deep;  the  washers, 
w,  w,  must  be  set  up  as  tight  as  the  threads  will  stand. 

The  spider,  s  (Figs.  9  and  10),  is  made  of  brass,  and  consists  of  a 
hub  (f  in.  diameter,  2  ins.  long,  and  f  in.  bore)  and  four  arms  having  T- 


shaped  ends,  the  wide  part  or  heads  of  which  project  beyond  the  arms 
and  hub  at  each  end,  the  length  of  these  heads  being  2j  ins.  and  their 
width  |  in.  The  heads  of  the  spider  arms  are  turned  off  to  fit  very 
closely  inside  the  drum,  r,  which  is  mounted  on  the  spider  in  such  a 
position  as  to  bring  the  spider  arms  in  alignment  with  the  lugs,  /,  of  the 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE 


ir 


drum;  screws  through  the  spider  arms  into  the  lugs  hold  the  drum  and 
spider  together. 

The  shaft,  5,  is  8J  ins.  long;  the  portion  j  is  ij  ins.  long  and  f  in. 
diameter;  k  is  i  in.  long  and  7-16  in.  diameter;  the  part  passing  through 
the  core  is  3  ins.  long  and  f  in.  in  diameter;  m  is  f  in.  long  and  7-16  in. 


FIG.  9 


FIG.  10 


FIG.  ii 


diameter;  and  p  is  3  ins.  long  and  f  in.  diameter.  The  spider,  s,  may  be 
secured  to  the  shaft  by  a  key  or  a  set-screw;  the  set-screw  is  sufficient  in 
so  small  a  machine.  The  commutator  (not  shown)  must  not  be  more  than 
|  in.  over  all,  along  the  shaft;  it  must  have  J  in.  brush  surface  and  24 
segments;  other  details  may  be  made  to  suit  the  will  of  the  builder.  The 


12  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

front  end  of  the  commutator  must  be  not  less  than  3-16  in.  from  the 
shoulder  where  j  and  k  join. 

The  armature  is  next  prepared  for  winding  by  removing  the  drum 
and  core  from  the  spider  and  insulating  the  ends  and  interior  of  the  core 
and  the  walls  of  the  slots.  Cut  four  rings  of  heavy  drilling  of  a  size  to 
cover  the  washers,  u>,  w,  and  the  ends  of  the  drum,  r ;  varnish  two  of  them 
on  one  side  with  shellac,  and  apply  them  to  the  ends  of  the  armature  body. 
While  these  are  hardening  cut  forty- eight  strips  of  drilling  ij  ins.  wide  and 
2\  ins.  long;  in  each  end  of  each  of  these  cut  two  slits  \  in.  long  parallel 
with  the  sides,  and  located  15-32  in.  from  each  side  of  the  strip.  Varnish 
these  on  one  side,  and  when  nearly  dry  fold  them  into  troughs  to  fit  the 
slots,  two  troughs  to  a  slot,  one  within  the  other;  fold  them  so  that  the 
varnish  will  be  on  the  inside  of  the  trough. 

When  these  are  dry  varnish  the  slots  and  the  outsides  of  the  troughs 
and  put  the  latter  in  the  slots,  bending  the  ends  flat  against  the  core  and 
securing  them  there  with  a  little  fresh  varnish.  Then  varnish  the  ends 
of  the  core  (two  cloth  rings  being  on  them),  and  one  side  of  the  two  re- 
maining rings  of  drilling;  put  these  rings  on  top  of  the  first  ones,  varnish 
them  on  the  outside,  and  put  the  core  in  an  oven  to  bake.  The  armature 
coils  consist  of  No.  24  double-silk-covered  wire,  wound  5  turns  wide  and 
14  layers  deep.  Before  winding  them  four  strips  of  wood  3  ins.  long, 
|  in.  wide,  and  J  in.  thick  should  be  screwed  to  the  inner  wall  of  the  brass 
drum,  in  line  with  the  lugs,  /,  so  as  to  preserve  the  spaces  for  the  four  arms 
of  the  spider.  A  double  thickness  of  drilling  should  also  be  applied  to 
the  interior  of  the  drum  to  insulate  the  coils  from  it.  The  connections 
are  the 'simple  Gramme  ring  arrangement. 

The  field  winding  is  necessarily  divided  into  two  coils,  on  account  of 
the  rear  bearing  passing  through  the  magnet.  Each  coil  consists  of  No. 
28  double-cotton-covered  wire,  wound  f  in.  deep  and  if  ins.  long;  the 
two  coils  are  connected  in  series  with  each  other  and  in  shunt  to  the  brushes. 
Heads  of  hard  fiber  \  in.  thick  should  be  used  to  protect  the  ends  of  each 
coil;  one  of  these  is  shown  by  H  (Fig.  12),  but  the  width  should  be  f  in. 
instead  of  j  in.  as  marked. 

It  is  in  two  pieces,  the  seams  being  at  the  ends,  and  is  cut  from  J  in. 
sheet  fiber.  The  two  halves  may  be  clamped  together  on  the  core  by 
means  of  a  small  brass  wire  drawn  around  the  outer  edge,  laying  in  a 
shallow  groove,  the  ends  being  twisted  and  cut  close.  The  pole-pieces 
should  be  removed  before  taping  and  putting  on  the  heads,  to  facilitate 
these  operations  as  well  as  the  winding  of  the  coil.  One  fiber  head  has  a 
notch,  n,  half  way  of  its  inner  long  side  to  enter  the  field  wire.  The  pole- 
pieces  should,  of  course,  be  removed  before  winding  the  field  coil,  and 
the  magnet  core  should  be  wrapped  with  two  layers  of  varnished  drilling 


ONE-SIXTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE 


where  the  coils  are  to  go.  The  entering  end  of  each  coil  should  be  remote 
from  the  journal,  and  this  means  that  the  magnet  must  be  turned  end 
for  end  after  one  coil  is  wound,  or  else  the  two  coils  must  be  wound  in 
opposite  directions  in  order  that  the  free  ends  at  the  center  of  the  magnet 
may  be  connected  together.  It  is  advisable  to  provide  a  starting  switch 
similar  to  the  one  shown  diagrammatically  by  Fig.  13,  where  F  is  the 
field  coil;  B  B  the  brushes;  5"  the  starting  switch  lever;  L  a  32-candle-power 
1 10- volt  lamp;  M  a  magnet,  and  SW  a  double-pole  snap  switch. 

The  motor  is  intended  to  be  mounted  on  a  wooden  base-board  8  ins. 
x  8  ins.,  a  cleat  3  ins.  wide  and  7-16  in.  thick  being  put  under  the  pole- 
pieces  so  as  to  clear  the  field  coil.  Bolts  from  beneath,  tapped  into  the 


tine 


FIG.  12 


FIG.  13 


magnet  and  countersunk  in  the  under  side  of  the  base,  should  be  used  to 
hold  the  motor  on  the  base.  The  pulley  may  be  any  diameter  from  i  in. 
to  3  ins.  by  i  in.  face,  if  crowned,  or  J  in.  if  grooved. 

WINDINGS    FOR   BATTERY   CURRENT 

For  6- volt  battery  current  the  armature  should  be  wound  with  12  coils 
of  No.  13  wire,  each  coil  having  16  turns  and  occupying  two  (adjacent) 
slots.  The  field  wire  should  be  No.  18,  wound  12  layers  deep  and  38 
turns  long  in  each  coil;  the  two  coils  containing  912  turns  in  all.  The 
commutator  must  have  12  segments  and  a  brush  surface  j  in.  wide;  copper 
brushes  f  x  J  in.  should  be  used,  the  contact  faces  being  cut  to  such  a 
bevel  as  to  present  a  surface  at  least  \  in.  square  each.  The  field  winding 
is  to  be  connected  in  shunt  to  the  brushes,  instead  of  in  series  as  is  usually 
the  practice  in  battery  motor  construction.  This  winding  is  for  6  volts  at 
the  terminals;  the  current  required  will  depend  upon  the  work  done;  the 
machine  is  capable  of  standing  an  armature  current  of  20  to  25  amperes. 


CHAPTER  III 
ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 

FIG.  14  represents  the  field  magnet  and  Fig.  15  one  of  the  journal  yokes 
of  a  J  horse-power  no- volt  motor,  with  a  drum  armature.  The  magnet 
is  of  the  familiar  single-coil  type.  The  core  is  of  round  machinery  steel, 
2\  ins.  in  diameter  and  9  ins.  long  over  all.  The  ends  are  turned  tapering 
as  indicated  by  dotted  lines,  to  insure  intimate  contact  with  the  yokes; 
the  taper  is  from  the  full  diameter  to  if  ins.,  and  begins  2  ins.  from  each 
end.  The  pole-pieces  are  of  cast  iron.  Fig.  16  gives  a  plan  view  and  a 
face  view  of  one  pole-piece,  from  which  all  the  essential  dimensions  may 
be  obtained.  The  arms  which  support  the  journal  yokes  are  cast  solid 
with  the  pole-pieces,  and  their  horizontal  thickness  tapers  from  J  in.  at  the 
pole-piece  to  J  in.  where  the  yoke  is  bolted  on. 

In  fitting  the  magnet  frame  together  the  best  procedure  is  to  bore  the 
tapered  holes  in  the  lower  part  of  each  pole-piece  and  turn  the  ends  of  the 
magnet  core  to  the  same  taper,  but  just  a  trifle  large;  then  dress  each 
taper  down  very  gradually  with  a  fine  file  (the  core  being  run  in  a  lathe) 
until  the  pole-piece  can  be  pushed  on  by  hand  far  enough  to  bring  the  end 
of  the  core  within  1-32  in.  of  the  back  surface  of  the  cast  iron.  The  pole- 
pieces  and  ends  of  the  core  should  be  punch-marked,  so  as  to  insure  finally 
mounting  each  pole-piece  on  the  end  to  which  it  was  fitted.  After  dressing 
down  the  ends  of  the  core  as  above  described,  drill  and  tap  in  each  end 
a  hole  for  a  J-in.  machine  screw,  the  purpose  of  which  will  be  apparent 
by  glancing  at  the  right-hand  end  of  the  magnet  in  Fig.  14,  where  C  is  a 
four-armed  claw  or  spider  with  a  hole  through  the  center  where  the  arms 
intersect.  The  arms  are  J  in.  thick,  measured  at  right  angles  to  the  bolt, 
and  taper  from  J  in.  to  J  in.  thick  measured  parallel  with  it.  One  of  these 
spiders  is  used  at  each  end,  though  the  drawing  shows  it  at  only  one  end 
of  the  machine. 

After  drawing  one  pole-piece  home  solid  by  means  of  its  spider  and 
bolt,  slip  the  other  pole-piece  on  loosely  and  clamp  the  pole-pieces  lightly 

14 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE      15 


FIG. 


FIG.  14 


i6 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


FIG.  16 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE      17 

between  two  iron  plates  with  planed  surfaces,  applied  between  the  journal 
arms,  so  as  to  keep  the  four  horns  of  the  pole-pieces  in  alignment;  then 
force  the  second  pole-piece  home  by  means  of  its  bolt  and  spider,  and 
clamp  the  horns  hard  between  the  iron  plates.  The  bottom  surfaces  of 
the  cast-iron  pieces  should  then  be  trued  up  on  a  planer  or  shaper  and  the 
clamps  taken  off  the  pole-piece  horns. 

The  next  operation  is  boring  the  armature  chamber  and  the  seats  for 
the  journal  yokes.  The  armature  chamber  bore  is  4  3-16  ins.;  the  seats 
for  the  journal  yokes,  marked  " finished  part"  in  Fig.  16,  are  bored  or  cut 
to  4§  ins.  diameter,  and  this  must  be  done  before  the  position  of  the  machine 
is  disturbed  after  boring  the  armature  chamber.  This  completes  the 
machine  work  on  the  magnet,  except  the  bolt  holes. 

The  journal  yoke  may  be  made  of  brass  or  any  composition  metal. 


FIG.  17 


The  bar  is  3-16  in.  thick  and  if  in.  wide,  except  near  the  ends,  where  it 
flares  to  correspond  with  the  width  of  the  arms.  At  each  end  is  a  right- 
angled  lug,  j-  in.  thick  after  machining;  these  lugs  fit  the  seats  in  the  ends 
of  the  iron  arms,  and  the  yokes  should  be  fitted  to  the  magnet  immediately 
after  finishing  the  machine  work  on  the  latter,  and  before  it  is  taken  apart 
to  put  on  the  coil.  The  box  portion  is  i  J  ins.  long  over  all,  3-16  in.  of  its 
length  being  on  the  inside  of  the  yoke  and  if  ins.  on  the  outside.  As 
shown  by  the  plan  view  of  the  yoke  in  Fig.  15,  there  are  stiffening  ribs 
starting  flush  near  the  ends  of  the  yoke  and  attaining  a  width  of  f  in.  at 
the  box;  these  are  3-16  in.  thick.  The  box  is  i  in.  in  outer  diameter,  and 
bored  to  f  in.  inside;  it  is  bushed  to  }  in.  diameter.  These  latter  dimen- 
sions, excepting  the  final  inside  diameter  of  the  bushing,  may  be  varied 


i8 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


to  suit  individual  ideas,  as  may  also  the  design  of  the  box.  The  only 
essential  measurements  are  those  of  the  yoke-bar,  the  length  of  the  box 
and  the  bore  of  the  journal  bushing.  The  journal  yokes  are  held  in  place 
by  J  in.  cap  screws  passing  through  the  iron  arms  and  tapping  into  the 
lugs  of  the  yokes. 

Figs.  17,  1 8,  and  19  show  the  shaft  and  armature  core  (the  latter  in 
cross- section),  an  armature  disc,  and  the  shell  and  head.  The  discs  are 
of  low-carbon  annealed  steel  4  ins.  outside  diameter  with  a  ij-in.  hole  in 
the  center  and  a  3-i6-in.  key-seat,  annealed  after  punching  and  key-seating; 
there  are  eighteen  slots  3-i6-in.  wide  and  J  in.  deep.  The  shell  and  one 
head  are  cast  in  one  piece  (of  brass),  and  consist  of  a  barrel  i  J  ins.  outside 
diameter  (when  finished)  and  2  ins.  long,  with  a  head,  s,  at  one  end,  3^  ins. 
in  diameter  and  tapered  in  thickness  from  J  in.  near  the  center  to  1-16  in. 
at  the  periphery;  at  the  opposite  end  of  the  barrel  is  a  cross-bar  J  in.  thick, 
cast  with  the  barrel  and  of  the  shape  shown,  being  f  in.  wide  where  it 

joins  the  barrel  and  f  in.  at  the  center. 
A  J-in.  hole  is  drilled  in  the  center  of 
this  cross-bar  and  another  in  the  cen- 
ter of  the  head,  5,  at  the  other  end  of 
the  barrel;  the  shell  is  mounted  on  a 
mandrel,  the  barrel  turned  down  to 
fit  the  hole  in  the  armature  discs,  and 
both  sides  of  the  head  faced  off 
smooth.  A  3-16  in.  key-seat  J  in. 
deep  is  cut  in  the  barrel  so  as  to  come 
in  the  center  of  one  end  of  the  cross- 
bar, as  shown ;  a  3- i6-in.  x  J-in.  parallel 
key  is  laid  in  the  key-seat,  and  the 
discs  threaded  on  the  barrel  and  com- 
pressed against  the  head  by  the  collar, 
h,  and  two  bolts  (not  shown)  passing 

through  the  collar  and  inside  the  barrel,  and  tapping  into  the  head  at  the 
other  end.  This  collar,  h,  is  of  brass,  3!  ins.  in  diameter  and  tapering 
from  3-16  to  1-16  in.  in  thickness  when  finished.  The  opening  in  the 
center  should  fit  the  outline  of  the  cross-bar  on  the  end  of  the  barrel  at 
least  closely  enough  to  prevent  the  collar  from  shifting  under  stress  of 
centrifugal  force;  the  collar  must  be  finished  up  smooth  on  both  sides. 
A  disc  of  insulation  should  be  put  on  next  to  the  brass  head  before  the  iron 
discs  are  put  on,  and  another  insulating  disc  should  go  between  the  last 
iron  disc  and  the  clamping  collar,  h. 

If  the  slots  are  cut  in  the  core  with  a  milling  machine  the  discs  must 
all  come  off  the  barrel  to  have  the  burrs  removed,  and  also  be  reannealed; 


FIG.  18 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE      19 

the  key-seat  will  insure  their  returning  in  the  original  angular  position. 
It  is  much  better  to  have  discs  with  the  slots  punched  before  the  first 
annealing.  The  shaft  is  lof  ins.  long  over  all;  j  in.  in  diameter  in  the 
largest  part,  f  in.  where  the  commutator  goes  and  J  in.  in  the  journals. 
A  i-i6-in.  x  J-in.  collar,  c,  is  shown  back  of  the  armature,  the  purpose  of 
which  is  merely  to  "locate"  the  armature  shell;  it  is  not  absolutely  neces- 
sary, however,  and  may  be  left  off  if  desired.  The  easiest  way  to  provide 
for  it  is  to  make  the  shaft  of  i-in.  stock,  leaving  the  original  metal  to  form 
the  collar  when  turning  the  shaft  to  proper  diameter.  The  armature 
shell  may  be  keyed  to  the  shaft  or  pinned  obliquely  through  the  thick  part 
of  the  head;  it  must  be  positively  secured  by  some  such  means. 

The  commutator  shell  must  be  bored  to  fit  the  f-in.  portion  of  the 
shaft,  and  must  not  exceed  ij  ins.  along  the  shaft.  The  lugs  where  the 
wires  are  attached  to  the  segments  may  project  toward  the  armature  J  in. 
or  so.  There  must  be  36  segments,  and  a  diameter  of  2  ins.  is  recom- 
mended. The  quadrant  carrying  the  brush  holders  should  be  fitted  to 
the  inner  end  of  the  journal  box,  and  carbon  brushes  not  smaller  than 


FIG.  19 

J  in.  x  J  in.  (one  on  each  side)  on  the  contact  surface  should  be  used. 
If  the  machine  be  used  as  a  dynamo  (it  will  maintain  five  or  six  no- volt 
lamps)  metal  brushes  of  the  same  surface  should  be  used  to  reduce  the 
resistance  of  the  brush  contact. 

The  field  coil  consists  of  No.  27  single-cotton-covered  wire,  wound  to 
an  outer  diameter  of  3!  ins.  After  the  magnet  is  fitted  as  described  in 
the  beginning  of  this  chapter  it  is  taken  apart  and  two  circular  magnet 
heads  of  fiber  J  in.  thick  and  3!  in.  outer  diameter  are  put  on  with  a  driving 
fit,  care  being  taken  that  the  distance  along  the  core  from  outside  to  outside 
of  the  heads  corresponds  with  the  distance  between  the  pole-pieces  when 
the  whole  is  assembled.  A  groove  must  be  cut  on  the  inner  face  of  one 


20  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

head  from  the  center  to  the  outer  edge  in  order  to  lead  out  the  starting 
end  of  the  field  wire,  and  this  must  be  covered  with  two  layers  of  oil  paper 
to  prevent  short-circuiting  the  successive  layers  of  the  coil.  The  core 
must  be  insulated  with  three  layers  of  shellacked  muslin  between  the  heads 
and  the  field  wire  put  on  evenly,  care  being  taken  not  to  "spread"  the 
heads;  the  winding  must  be  very  carefully  done  so  as  to  get  in  as  many 
turns  as  possible  in  order  to  keep  down  the  heat  loss. 

After  winding  the  coil  and  securing  the  ends  one  pole-piece  is  put  on 
solid  and  the  other  one  slipped  on  until  it  begins  to  bind,  when  the  journal 
yokes  must  be  inserted  between  their  arms  and  the  bolts  put  in  as  far  as 
possible  without  jamming.  Then  by  tightening  up  the  journal  yoke  bolts 
and  the  pole-piece  bolt  together,  being  particular  never  to  draw  the  yoke 
bolt  hard  against  the  arm,  the  frame  will  come  together  in  its  original 
position.  As  an  additional  precaution  it  may  be  set  on  a  true  plane  surface, 
and  if  the  base  of  the  loose  pole-piece  gets  out  of  alignment  tap  the  horn 
lightly  until  the  frame  is  true  on  the  bottom.  The  magnet  frame  must 
be  provided  with  a  non-magnetic  base;  hard  wood  is  as  good  as  anything, 
the  frame  being  secured  by  flat-head  brass  machine  screws  from  below, 
two  in  each  casting,  countersunk  in  the  wood. 

The  armature  winding  is  divided  into  36  coils,  each  having  16  turns 
of  No.  23  double-cotton-covered  wire,  4  turns  wide  and  4  turns  deep 
in  the  slot.  The  slots  must  be  insulated  with  troughs  of  muslin  and  mica, 
or  preferably  flexible  micanite,  0.03  in.  thick.  The  troughs  are  easily 
made  by  cutting  the  material  into  strips  2\  ins.  long  by  ij  ins.  wide,  and 
slitting  the  ends  so  as  to  permit  the  projecting  portion  of  the  trough  to  be 
folded  back  flat  against  the  core.  Before  putting  in  the  troughs  a  disc  of 
heavy  drilling  3-^-  ins.  in  diameter  should  be  secured  to  each  end  of  the  core 
by  means  of  varnish,  and  the  outer  faces  varnished  and  allowed  to  nearly 
dry.  Then  put  in  the  troughs  and  put  on  two  more  muslin  discs,  var- 
nishing the  whole,  and  bake  until  thoroughly  dry.  Instead  of  winding 
each  coil  in  diametrically  opposite  slots,  take  slots  lacking  one  of  being 
precisely  opposite. 

A  good  plan  is  to  make  a  sketch  of  an  armature  disc  and  number  the 
slots  from  left  to  right  successively  around  the  periphery.  Then  wind 
the  coils  as  follows,  the  coil  numbers  indicating  the  order  in  which  the 
coils  are  put  on,  not  the  order  in  which  they  are  connected  to  the  com- 
mutator. 

COIL  NO. —    i     2.3     4     5     6     7     8     9   10   n    12   13   14   15    16   17   18 

COIL  NO. —  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36 

STARTS  IN  SLOT  NO. —  I  IO  13   4   7  16   2  II  15   6  14  .5  18   9   3  12   8  17 
ENDS  IN  SLOT  NO. —  9  l8   3  12  15   6  IO   I   5  14   4  13   8  17  II   2  l6   7 

Ench  pair  of  coils  must  be  covered  with  muslin  where  they  cross  the 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE      21 

heads  before  the  next  pair  is  put  on,  and  before  coil  No.  8  is  wound  on  top 
of  coil  No.  i  in  slot  No.  i  the  bottom  coil  must  be  insulated  by  a  strip  of 
micanite  laid  in  the  slot;  this  is  true  of  every  bottom  coil. 

After  the  winding  is  on,  and  before  connecting  up  to  the  commutator, 
the  band  wires  should  be  put  on.  Use  No.  19  B.  W.  G.  soft  tinned-iron 
wire,  known  by  hardware  dealers  as  "  white  stove-pipe  wire,"  for  the 
bands,  and  put  them  on  under  as  heavy'  pressure  as  possible  without 
endangering  the  armature  shaft.  Two  bands  of  eight  turns  each,  \  in. 
from  each  end  of  the  core,  will  suffice.  A  strip  of  mica  between  two  strips 
of  fullerboard  must  go  under  each  band,  and  the  bands  should  be  soldered 
at  intervals,  not  all  the  way  around.  Four  tin  clips  located  equidistantly, 
with  a  dab  of  solder  at  each,  will  give  ample  security. 

Care  must  be  taken  in  connecting  up  the  armature  winding  to  take  the 
starting  ends  of  the  coils  in  proper  succession  to  the  commutator  segments; 
the  outer  end  of  each  coil  goes  to  the  segment  on  the  right  of  the  one  to 
which  the  starting  end  is  led. 

The  principal  data  for  this  machine  are  as  follows: 

TERMINAL    E.    M.    F.,    IIO    VOLTS 

Armature  current,  normal    2  amps. 

Magnetic  flux  per  square  inch: 

In  field  core    100,000  lines 

In  pole-pieces 43,500     " 

In  air-gap 28,000     ' 

In  armature  teeth 80,000     ' 

In  armature  core 62 ,000     " 

Coefficient  of  leakage    1.4 

Commercial  efficiency  (friction  10  p.  c.  estimated) 60% 

Revolution  per  minute    2,000 


CHAPTER  IV 
ONE-FOURTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE 

THIS  machine  has  a  field  magnet  of  exactly  the  same  design  as  the 
one  last  described,  the  only  difference  being  in  the  dimensions.  The 
instructions  for  fitting  up  the  magnet  shown  by  Figs.  14  and  15,  therefore, 
apply  to  this  one.  The  size  of  the  magnet  core  and  yokes  shown  by  Fig. 
14  also  apply  to  this  magnet.  Figs.  21  and  22  give  all  of  the  dimensions 
for  this  magnet  frame  that  differ  from  those  of  the  previous  one,  excepting 
the  bore  of  the  armature  chamber,  which  is  5  3-16  ins.  instead  of  4  3-16 
ins.  The  lugs  that  support  the  journal  yokes  are  set  one  inch  wider  apart 
than  in  the  drum  armature  motor,  and  the  seats  for  the  ends  of  the  journal 
yokes  are  bored  or  cut  to  5!  ins.  diameter.  As  in  the  former  case,  this 
boring  must  be  done  before  the  frame  is  moved  from  the  position  it  occupied 
during  the  boring  of  the  armature  chamber. 

The  journal  yokes  may  be  made  of  any  metal  except  iron  and  steel. 
The  bar  is  3-16  in.  thick  and  ij  ins.  wide,  except  near  the  ends,  where  it 
flares  to  correspond  with  the  width  of  the  arms.  At  each  end  is  a  right- 
angled  lug,  £  in.  thick  after  machining;  these  lugs  fit  the  seats  in  the  ends 
of  the  iron  arms,  and  the  yokes  should  be  fitted  to  the  magnet  immediately 
after  finishing  the  machine  work  on  the  latter,  and  before  it  is  taken  apart 
to  put  on  the  coil.  The  box  portion  is  ij  ins.  long  over  all,  3-16  in.  of 
its  length  being  on  the  inside  of  the  yoke  and  i  J  ins.  on  the  outside.  As 
shown  by  the  plan  view  of  the  yoke,  Fig.  22,  there  are  stiffening  webs 
starting  flush  near  the  ends  of  the  yoke  and  attaining  a  width  of  j  in.  at 
the  box;  these  are  3-16  in.  thick.  The  box  is  i  in.  in  outer  diameter,  and 
bored  to  f  in.  inside;  it  is  bushed  to  f  in.  diameter.  Most  of  the  dimen- 
sions of  the  yoke  and  box  may  be  varied  to  suit  individual  ideas,  as  may 
also  the  design  of  the  box.  The  only  essential  measurements  are  the 
length  of  the  yoke-bar,  the  length  of  the  box,  and  the  bore  of  the  journal 
bushing.  The  journal  yokes  are  held  in  place  by  J-in.  cap  screws  passing 
through  the  iron  arms  and  tapping  into  the  lugs  of  the  yokes. 

22 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE     23 


FIG.  22 


FIG.  20 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


Finished 

<— K^ 


Finished 


FIG.  21 


ONE-FOURTH  HORSE-POWER  MOTOR  WITH  RING  ARMATURE     25 

The  armature  core,  spider,  and  shaft  are  shown,  partly  in  cross-section, 
by  Figs.  23  and  24.  The  core  is  built  up  of  low-carbon  annealed  steel 
discs  5  ins.  outside  diameter  and  2§  ins.  inside,  not  more  than  25  mils 
thick;  these  are  assembled  on  a  brass  drum  if  ins.  long  (Fig.  25)  which 
should  be  2j  ins.  outside  diameter  before  finishing,  so  that  it  may  be 


FIG.  23 


FIG.  24 


FIG.  25 


turned  down  to  exactly  fit  the  inner  circle  of  the  armature  rings;  the  wall 
of  the  drum  is  J  in.  thick  after  finishing,  and  there  are  four  equidistant 
projecting  lugs,  /,  f  in.  wide  and  \  in.  long,  on  each  end,  by  which  the 
drum  is  secured  to  the  spider  (see  Figs.  22  and  23).  The  rings  forming 
the  core,  c  (Fig.  23),  are  compressed  and  held  on  the  drum,  r,  by  two 
brass  washers,  w,  w,  3-16  in.  thick  and  3!  ins.  outer  diameter,  which  screw 


26  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


onto  the  lugs  and  ends  of  the  drum.  The  core  has  24  slots  J  in.  wide  and 
J  in.  deep,  and  when  compressed  it  is  ij  ins.  long.  The  washers,  w  w, 
must  be  set  up  as  tight  as  the  threads  will  stand. 

The  spider,  5  (Figs.  23  and  24),  is  made  of  brass,  and  consists  of  a  hub 
(|  in.  in  diameter,  2\  ins.  long,  and  f  in.  bore)  and  four  arms  having  T- 
shaped  ends,  the  wide  part  or  heads  of  which  project  beyond  the  arms 
at  each  end,  the  length  of  these  heads  being  2§  ins.  and  their  width  f  in. 
The  heads  of  the  spider  arms  are  turned  off  to  fit  very  closely  inside  the 
drum,  r,  which  is  mounted  on  the  spider  in  such  a  position  as  to  bring 
the  spider  arms  in  alignment  with  the  lugs,  /,  of  the  drum;  screws  through 
the  spider  arms  into  the  lugs  hold  the  drum  and  spider  together. 

The  shaft,  5,  is  8J  ins.  long;  the  portion  a  is  2j  ins.  long  and  f  in.  in 
diameter;  b  is  J  in.  long  and  J  in.  in  diameter;  the  part  passing  through 
the  core  is  2\  ins.  long  and  i  in.  in  diameter;  d  is  ij  ins.  long  and  f  in. 
in  diameter,  and  e  is  ij  ins.  long  and  f  in.  in  diameter.  The  spider,  s, 
should  be  secured  to  the  shaft  by  a  key,  the  key-seat  being  located  at  the 
base  of  one  of  the  arms.  The  front  end  of  the  commutator  must  be  located 
not  less  than  3-16  in.  from  the  shoulder  where  d  and  e  join. 

The  armature  is  next  prepared  for  winding  by  removing  the  drum  and 
core  from  the  spider  and  insulating  the  ends  and  interior  of  the  core  and  the 
walls  of  the  slots.  Cut  four  rings  of  heavy  drilling  of  a  size  to  cover  the 
washers,  w  w,  and  the  ends  of  the  drum,  r\  varnish  two  of  them  on  one 
side  with  shellac,  and  apply  them  to  the  ends  of  the  armature  body.  While 
these  are  hardening  cut  twenty  strips  of  micanite  cloth,  25-1000  in.  thick, 
i  5-16  ins.  wide  and  2  ins.  long;  in  each  end  of  each  of  these  cut  two  slits, 
\  in.  long,  parallel  with  the  sides  and  located  each  J  in.  from  the  center 
of  the  strip.  Varnish  these  on  one  side,  and  when  nearly  dry  fold  them 
into  troughs  to  fit  the  slots;  fold  them  so  that  the  varnish  will  be  on  the 
inside  of  the  trough. 

When  these  are  dry  varnish  the  slots  and  the  outsides  of  the  troughs 
and  put  the  latter  in  the  slots,  bending  the  ends  flat  against  the  core  and 
securing  them  there  with  a  little  fresh  varnish.  Then  varnish  the  ends 
of  the  core  (two  cloth  rings  being  on  them),  and  one  side  of  the  two  re- 
maining rings  of  drilling;  put  these  rings  on  top  of  the  first  ones,  varnish 
them  on  the  outside  and  put  the  core  in  an  oven  to  bake.  The  armature 
coils  consist  of  No.  22  double-cotton-covered  wire,  wound  6  turns  wide 
and  13  layers  deep.  Before  winding  them  four  strips  of  wood  3  ins. 
long,  |  in.  wide,  and  \  in.  thick  should  be  screwed  to  the  inner  wall  of  the 
brass  drum,  in  line  with  the  lugs,  /,  so  as  to  preserve  spaces  for  the  four 
arms  of  the  spider.  A  double  thickness  of  drilling  should  also  be  applied 
to  the  interior  of  the  drum  to  insulate  the  coils  from  it.  The  connections 
are  the  simple  Gramme  ring  arrangement.  Before  connecting  up  to  the 


ONE-FOURTH  HORSE-POWER  MOTOR   WITH  RING  ARMATURE     27 

commutator  the  band  wires  should  be  put  on.  Use  No.  19  B.  W.  G. 
soft  tinned-iron  wire,  known  by  hardware  dealers  as  "  white  stove-pipe 
wire,"  for  the  bands,  and  put  them  on  under  as  heavy  pressure  as  possible 
without  endangering  the  armature  shaft.  Two  bands  of  eight  turns  each, 
|  in.  from  each  end  of  the  core,  will  suffice.  A  strip  of  mica  between  two 
strips  of  fullerboard  must  go  under  each  band,  and  the  bands  should  be 
soldered  at  intervals,  not  all  the  way  around.  Four  tin  clips  located 
equidistantly,  with  a  dab  of  solder  at  each,  will  give  ample  security. 

The  commutator  (not  shown)  must  be  bored  to  fit  the  f-in.  portion,  d, 
of  the  shaft,  and  must  not  exceed  ij  ins.  along  the  shaft;  it  must  have  a 
brush  tread  i  in.  wide.  The  lugs  where  the  wires  are  attached  to  the 
segments  may  project  toward  the  armature  J  in.  or  so.  There  must  be 
24  segments,  and  a  diameter  of  2  ins.  is  recommended.  The  quadrant 
carrying  the  brush-holders  should  be  fitted  to  the  inner  end  of  the  journal 
box,  and  carbon  brushes  not  smaller  than  J  in.  x  f  in.  (one  on  each  side) 
on  the  contact  surface  should  be  used.  If  the  machine  be  used  as  a  dynamo 
(it  will  maintain  five  or  six  no- volt  lamps)  metal  brushes  of  the  same 
surface  should  be  used  to  reduce  the  resistance  of  the  brush  contact. 

The  field  coil  consists  of  No.  28  single-cotton-covered  wire,  wound  to 
a  depth  of  f  in.  After  the  magnet  is  fitted  as  described  in  the  beginning 
of  the  chapter,  it  is  taken  apart  and  two  circular  magnet  heads  of  fiber 
J  in.  thick  and  3!  ins.  outer  diameter  are  put  on  with  a  driving  fit,  care 
being  taken  that  the  distance  along  the  core  from  outside  to  outside  of  the 
heads  corresponds  with  the  distance  between  the  pole-pieces  (5  ins.),  when 
the  whole  is  assembled.  A  groove  must  be  cut  on  the  inner  face  of  one 
head  from  the  center  to  the  outer  edge,  in  order  to  lead  out  the  starting 
end  of  the  field  wire,  and  this  must  be  covered  with  two  layers  of  oil  paper 
to  prevent  short-circuiting  the  successive  layers  of  the  coil.  The  core 
must  be  insulated  with  three  layers  of  shellac  muslin  between  the  heads, 
and  the  field  wire  put  on  evenly,  care  being  taken  not  to  "spread"  the 
heads.  The  exact  number  of  turns  is  not  a  vital  matter,  but  it  should  be 
as  great  as  practicable  so  as  to  keep  down  the  heat  loss. 

After  winding  the  coil  and  securing  the  ends  one  pole-piece  is  put  on 
solid  and  the  other  one  slipped  on  until  it  begins  to  bind,  when  the  journal 
yokes  must  be  inserted  between  their  arms,  and  the  bolts  put  in  as  far  as 
possible  without  jamming.  Then  by  tightening  up  the  journal-yoke  bolts 
and  the  pole-piece  bolt  together,  being  particular  never  to  draw  the  yoke 
bolt  hard  against  the  arm,  the  frame  will  come  together  in  its  original 
position.  As  an  additional  precaution  it  may  be  set  on  a  true  plane  surface, 
and  if  the  base  of  the  loose  pole-piece  gets  out  of  alignment  tap  the  horn 
lightly  until  the  frame  is  true  on  the  bottom.  The  magnet  frame  must 
be  provided  with  a  non-magnetic  base;  hardwood  is  as  good  as  anything, 


28 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


the  frame  being  secured  by  flat-head  brass  machine  screws  from  below, 
two  in  each  casting,  countersunk  in  the  wood. 

The  principal  data  for  the  machine  are  as  follows: 

TERMINAL  E.  M.   F.,    IIO  VOLTS 

Armature  current,  normal    2  amps 

Commercial  efficiency  (windage  and  friction  losses  estimated)     60% 
Revolutions  per  minute 2,000 


lamps 


FIG.  26 


It  is  advisable  to  provide  a  starting  switch  similar  to  the  one  shown 
diagrammati.cally  by  Fig.  26,  where  b  b  are  the  brushes;  S  the  starting 
switch  lever;  m  a  magnet,  and  Sw  a  double-pole  snap  switch.  The  lamps 
shown  are  50- volt,  32  candle-power  lamps.  The  handle  of  the  starting 
switch  is  provided  with  a  spring  tending  to  keep  it  in  the  position  shown 
by  the  sketch.  This  starting  switch  is  also  suitable  for  use  with  the  motor 
described  in  Chapter  III. 


CHAPTER  V 
ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 

FOR  this  size  of  motor  three  types  of  field  magnet  are  described:  the 
single-coil,  like  those  previously  described,  a  bipolar  one-piece  magnet  of 


FIG.  27 

the  Lahmeyer  type,  and  a  similar  form  with  four  poles  (Kapp  type).    The 
armature  core  and  shaft  are  the  same  in  each  case,  excepting  the  number 

29 


3o  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

of  slots  in  the  armature  of  the  four-pole  machine.  The  machine  is  a 
£  horse-power  motor  to  operate  on  a  no- volt  constant  potential  circuit 
at  a  speed  of  2,000  revolutions  per  minute.  The  single-coil  magnet 
(Figs.  27  and  28)  has  a  round  core  of  commercial  wrought  iron  2|  ins.  in 
diameter  and  n  ins.  long  over  all.  The  ends  are  turned  tapering,  as 
indicated  by  the  dotted  lines,  to  insure  intimate  contact  with  the  yokes; 


FIG.  28 

the  taper  is  from  the  full  diameter  to  2\  ins.,  and  begins  2\  ins.  from  each 
end.  The  pole-pieces  are  of  cast  iron.  The  arms  which  support  the 
journal  yokes  are  cast  solid  with  the  pole-pieces,  and  their  horizontal 
thickness  tapers  from  J  in.  at  the  pole-piece  to  \  in.  where  the  yoke  is 
belted  in  place. 


ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 


In  fitting  the  magnet  frame  together  the  best  procedure  is  to  bore  the 
tapered  holes  in  the  lower  part  of  each  pole-piece  and  turn  the  ends  at 
the  magnet  core  to  the  same  taper,  but  just  a  trifle  larger;  then  dress  each 
tapered  end  of  the  core  down  very  gradually  with  a  fine  file  (the  core 
being  run  on  a  lathe)  until  the  pole-piece  can  be  pushed  on  by  hand  far 
enough  to  bring  the  end  of  the  core  within  3-64  in.  of  the  surface  of  the 
cast  iron.  The  pole-pieces  and  ends  of  the  core  should  be  punch-marked 
so  as  to  insure'  finally  mounting  each  pole-piece  on  the  end  which  was 
fitted  to  it.  After  dressing  down  the  ends  of  the  core  as  above  described 
drill  and  tap  in  each  end  a  hole  for  a  J-in.  machine  screw,  the  purpose  of 
which  will  be  made  apparent  by  a  glance  at  the  right-hand  end  of  the 
complete  magnet  in  Fig.  27,  where  C  is  a  four-armed  claw  or  spider,  with 
a  hole  through  the  center  where  the  arms  intersect.  The  arms  are  J  in. 
thick,  measured  at  right  angles  to  the  bolt,  and  taper  from  3-16  to  f  in. 
thick,  measured  parallel  with  it.  One  of  these  claws  or  spiders  is  used  at 
each  end  of  the  core,  though  the  drawing  shows  it  at  one  end  only. 

After  drawing  one  pole-piece  home  solid  by  means  of  the  spider  and 
bolt,  slip  the  other  on  the  other  end 

of  the  core   loosely  and  clamp  the    ,  /t  , 

pole-pieces  lightly  between  two  iron 
plates  with  planed  surfaces,  applied 
between  the  journal  arms,  so  as  to 
keep  the  four  horns  of  the  pole-pieces 
in  alignment;  then  force  the  second 
pole-piece  home  and  clamp  the  horns 
hard  between  the  iron  plates.  The 
bottom  surface  of  the  pole-pieces  are 
then  to  be  turned  up  on  a  shaper  or 
planer  and  the  iron  clamping  plates 
removed  from  the  horns. 

The  next  operation  is  boring  the 
armature  chamber  and  the  seats  for 

the  ends  of  the  journal  yokes.  The  bore  of  the  armature  chamber  is 
4  3-16  ins.;  the  seats  for  the  journal  yokes  are  machined  to  a  4§-in.  circle 
for  |  in.  from  the  outer  ends.  These  operations  must  be  completed 
before  the  original  position  of  the  frame  on  the  lathe  or  boring  machine 
is  altered.  This  completes  the  machine  work  on  the  magnet,  with  the 
exception  of  the  holes  through  the  ends  of  the  supporting  arms  and  holes 
in  the  bottom  surfaces  of  the  pole-pieces  for  bolting  to  the  base. 

The  journal  yoke  must  be  made  of  brass  or  some  similar  composition. 
The  bar  is  3-16  in.  thick  and  ij  ins.  wide,  except  near  the  ends,  where  it 
flares  to  correspond  with  the  width  of  the  supporting  arms.  At  each  end 


FIG.  29 


32  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

is  a  right-angle  lug,  3-16  in.  thick  after  machining;  these  lugs  fit  the  ma- 
chined seats  in  the  ends  of  the  iron  arms,  and  the  yokes  should  be  fitted 
to  these  arms  before  the  frame  is  taken  apart  to  put  on  the  magnet  coil. 
The  journal  box  is  2  ins.  long  over  all,  f  in.  of  its  length  projecting  on  the 
inside  of  the  yoke  bar,  and  i  7-16  ins.  on  the  outside.  As  shown  by  the 
plan  view  of  the  yoke  in  Fig.  29,  there  are  stiffening  ribs  starting  flush 
near  the  ends  of  the  yoke  and  attaining  a  height  of  f  in.,  where  they  join 
the  box;  these  ribs  are  3-16  in.  thick.  The  box  is  i  J  ins.  in  outside  diameter 
and  bored  out  f  in.;  the  bore  is  bushed  to  f  in.  No  particular  form 
of  oiling  device  is  specified,  as  any  amateur  of  sufficient  ability  to  build 
such  a  motor  will  be  fully  competent  to  decide  this  detail  for  himself. 
The  journal  yokes  are  held  in  place  by  J-in.  cap-screws  passing 
through  the  ends  of  the  supporting  arms  and  tapping  into  the  lugs  on  the 
yokes. 

The  field  coil  consists  of  No.  26  single-cotton-covered  magnet  wire, 
wound  to  a  depth  of  i  in.  After  the  magnet  is  fitted  as  described  it  is 
taken  apart  and  two  circular  fiber  heads  4j  ins.  in  diameter  and  J  in.  thick 
are  put  on  the  core  with  a  driving  fit,  care  being  taken  that  the  distance 
from  outside  to  outside  of  the  heads  corresponds  with  the  space  between 
the  perpendicular  faces  of  the  pole-pieces  when  the  frame  is  assembled; 
this  measurement  should  be  taken  prior  to  dismantling  the  frame.  A 
groove  must  be  cut  on  the  outer  face  of  one  head,  from  the  center  to  the 
outer  edge,  in  order  to  form  a  channel  for  leading  out  the  starting  ends 
of  the  coil  when  the  frame  is  reassembled,  at  which  time  two  discs  of  oil 
paper  with  one  of  mica  between  them  must  be  threaded  on  the  core  outside 
of  this  head  to  insulate  the  leading-out  wire  from  the  pole-piece.  Before 
winding  the  coil  insulate  the  core  with  a  strip  of  muslin  just  wide  enough 
to  go  between  the  heads,  and  long  enough  to  wrap  around  the  core  three 
times;  this  should  be  heavily  shellacked  before  it  goes  on.  The  coil  must 
be  carefully  wound  so  as  to  get  in  as  many  turns  as  possible  without  jamming 
the  insulation,  in  order  to  keep  down  the  heat  loss. 

After  winding  the  coil  and  securing  the  ends,  put  one  pole-piece  on 
solid  and  slip  the  other  on  loosely.  When  it  begins  to  bind  bolt  the  journal 
yoke  to  the  lugs  on  the  pole-piece  first  put  on,  and  insert  the  bolts  through 
the  lugs  of  the  one  that  is  loose.  Then  tighten  up  the  spider  bolt  at  the 
end  of  the  core  and  force  it  into  place,  the  bolts  through  the  lugs  serving 
as  guides  to  keep  the  pole-piece  from  twisting  on  the  core.  These  bolts 
should  be  set  up  little  by  little  with  the  spider  bolt,  so  as  to  keep  the  bolt 
heads  within  1-16  in.  of  the  surface  of  the  lugs.  As  an  additional  pre- 
caution the  frame  may  be  set  on  a  true  surface  and  tried  at  intervals  to 
see  if  it  gets  out  of  alignment;  if  it  does,  tap  the  horn  of  the  loose  pole- 
piece  until  the  bottom  surface  agrees  with  the  guide.  The  magnet  frame 


ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE         33 

must  be  provided  with  a  non- magnetic  base,  preferably  composition  metal, 
but  allowably  of  wood. 

Figs.  30,  31,  and  32  show  an  armature  disc,  the  shaft  and  armature 
core  (the  latter  in  cross-section),  and  the  shell  and  head.  The  discs  are 
of  charcoal  iron,  4  ins.  outside  diameter,- with  a  i-in.  hole  in  the  center  and 
a  J-in.  key-seat,  annealed  after  punching  and  key-seating;  there  are 
1 8  slots  3-16  in.  wide  and  \  in.  deep.  The  shell  and  one  head  are  cast  in 
one  piece  (of  brass),  and  consist  of  a  barrel  i  in.  outside  diameter  (when 
finished),  and  2  ins.  long,  with  a  head,  s,  at  one  "end,  3!  ins.  in  diameter 
and  tapered  in  thickness  from  \  in.  near  the  center  to  1-16  in.  at  the  pe- 
riphery; at  the  opposite  end  of  the  barrel  is  a  cross-bar  J  in.  thick,  cast 
with  the  barrel  and  of  the  shape  shown,  being  f  in.  wide  where  it  joins 
the  barrel  and  j  in.  at  the  center.  A  J-in.  hole  is  drilled  in  the  center  of 
this  cross-bar  and  another  in  the  center  of  the  head,  s,  at  the  other  end  of 


the  barrel;  the  shell  is  mounted  on  a  mandrel,  the  barrel  is  turned  down 
to  fit  the  hole  in  the  armature  discs,  and  both  sides  of  the  head  are  faced 
off  smooth.  A  J-in.  key-seat  3-16  in.  deep  is  cut  in  the  barrel,  so  as  to 
come  in  the  center  of  one  end  of  the  cross-bar,  as  shown;  a  J-in.  x  J-in. 
feather,  or  parallel  key,  is  laid  in  the  key-seat,  and  the  discs  are  threaded 
on  the  barrel  and  compressed  against  the  head  by  the  collar,  /*,  drawn 
down  by  two  bolts  (not  shown)  passing  through  the  collar  and  inside  the 
barrel,  and  tapping  into  the  head  at  the  other  end.  This  collar,  h,  is  of 
brass,  3!  ins.  in  diameter  and  tapering  from  3-16  to  1-16  in.  in  thickness 
when  finished.  The  opening  in  the  center  should  fit  the  outline  of  the 
cross-bar  on  the  end  of  the  barrel  at  least  closely  enough  to  prevent  the 
collar  from  shifting  under  stress  of  centrifugal  force;  the  collar  must  be 
finished  up  smooth  on  both  sides.  A  disc  of  insulation  should  be  put  on 


34 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


next  to  the  brass  head  before  the  iron  discs  are  put  on,  and  another  insu- 
lating disc  should  go  between  the  last  iron  disc  and  the  clamping  collar,  h. 
If  the  slots  are  cut  in  the  core  with  a  milling  machine  the  discs  must 
all  come  off  the  barrel  to  have  the  burrs  removed,  and  also  be  reannealed; 
the  key-seat  will  insure  their  returning  in  the  original  angular  position. 
It  is  much  better  to  have  discs  with  the  slots  punched  before  the  first 
annealing.  The  shaft  is  nf  ins.  long  over  all;  i  in.  in  diameter  in  the 
largest  part;  J  in.  where  the  commutator  goes,  and  f  in.  in  the  journals. 
A  i-i6-in.  x  J-in.  collar,  e,  is  shown  back  of  the  armature,  the  purpose  of 
which  is  merely  to  "locate"  the  armature  shell;  it  is  not  absolutely  neces- 
sary, however,  and  may  be  left  off  if  desired.  The  easiest  way  to  provide 
for  it  is  to  make  the  shaft  of  ij-in.  stock,  leaving  the  original  metal  to 
form  the  collar  when  turning  the  shell  to  the  proper  diameter.  The 
armature  shell  may  be  keyed  to  the  shaft  or  pinned  obliquely  through  the 


FIG.  30 


FIG.  32 


thick  part  of  the  head;  it  must  be  positively  secured  by  some  such  means. 
The  commutator  shell  must  be  bored  to  fit  the  f-in.  portion  of  the 
shaft,  and  must  not  exceed  ij  ins.  along  the  shaft.  The  lugs  where  the 
wires  are  attached  to  the  segments  may  project  toward  the  armature  J  in. 
or  so.  There  must  be  36  segments,  and  a  diameter  of  2j  ins.  is  recom- 
mended. The  quadrant  carrying  the  brush  holders  should  be  fitted  to 
the  inner  end  of  the  journal  box,  and  carbon  brushes  (one  on  each  side) 
not  smaller  than  f  in.  x  J  in.  on  the  contact  surface  should  be  used.  If 
the  machine  be  used  as  a  dynamo  (it  will  maintain  about  ten  no- volt 
lamps)  metal  gauze  brushes  of  the  same  surface  may  be  used  to  reduce  the 
resistance  of  the  brush  contact,  but  it  is  not  strictly  necessary.  The  arma- 
ture winding  is  divided  into  36  coils,  each  having  16  turns  of  No.  20  double- 
cotton-covered  wire,  4  turns  wide  and  4  turns  deep  in  the  slot.  The 
slots  must  be  insulated  with  troughs  of  muslin  and  mica,  or  preferably 


ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE         35 

flexible  micanite,  0.03  in.  thick.  The  troughs  are  easily  made  by  cutting 
the  material  into  strips  2\  ins.  long  by  ij  ins.  wide,  and  slitting  the  ends 
so  as  to  permit  the  projecting  portion  of  the  trough  to  be  folded  back  flat 
against  -the  core.  Before  putting  in  the  troughs  a  disc  of  heavy  drilling 
3  ins.  in  diameter  should  be  secured  to  each  end  of  the  core  by  means  of 
varnish,  and  the  outer  faces  varnished  and  allowed  to  nearly  dry.  Then 
put  in  the  troughs  and  put  on  two  more  muslin  discs,  varnishing  the  whole, 
and  bake  until  thoroughly  dry.  Instead  of  winding  each  coil  in  diamet- 
rically opposite  slots,  take  slots  lacking  one  of  being  precisely  opposite. 

A  good  plan  is  to  make  a  sketch  of  an  armature  disc  and  number  the 
slots  from  left  to  right  successively  around  the  periphery.  Then  wind  the 
coils  as  follows,  the  coil  numbers  indicating  the  order  in  which  the  coils  are 
put  on,  not  the  order  in  which  they  are  connected  to  the  commutator: 

COIL  NO. —    i     2     3     4     5     6     7     8     9   10   ii    12   13   14   15   16  17   18 
COIL  NO. —  19  20  21   22   23  24  25   26  27  28  29  30  31   32  33  34  35  36 

STARTS  IN  SLOT  NO.  —   I  IO  13   4   7  16   2  II  15   6  14   5  l8   9   3  12   8  17 
ENDS  IN  SLOT  NO. —  9  l8   3  12  15   6  IO   I   5  14   4  13   8  17  II   2  16   7 

Each  pair  of  coils  must  be  covered  with  muslin  where  they  cross  the 
heads  before  the  next  pair  is  put  on,  and  before  coil  No.  8  is  wound  on  top 
of  coil  No.  i  in  slot  No.  i  the  bottom  coil  must  be  insulated  by  a  strip  of 
micanite  laid  in  the  slot;  this  is  true  of  every  bottom  coil. 

After  the  winding  is  on,  and  before  connecting  up  to  the  commutator, 
the  band  wires  should  be  put  on.  Use  No.  19  B.  W.  G.  soft  tinned-iron 
wire,  known  by  hardware  dealers  as  "  white  stove-pipe  wire,"  for  the 
bands,  and  put  them  on  under  as  heavy  pressure  as  possible  without 
endangering  the  armature  shaft.  Two  bands  of  eight  turns  each,  \  in. 
from  each  end  of  core,  will  suffice.  A  strip  of  mica  between  two  strips  of 
fullerboard  must  go  under  each  band,  and  the  bands  should  be  soldered 
at  intervals,  not  all  the  way  around.  Four  tin  clips  located  equidistantly, 
with  a  dab  of  solder  at  each,  will  give  ample  security. 

If  cast  steel  be  available,  one  of  the  iron-clad  types  of  magnet,  shown 
by  Figs.  33  and  34,  is  somewhat  preferable  because  of  the  small  amount  of 
machine  work  required.  Of  these  two  the  four-polar  type  is  considered 
preferable  by  the  writer,  being  much  lighter  in  weight,  and  having  an 
" open-head"  armature  winding.  Each  of  the  iron-clad  magnets  is  a 
single  casting;  the  essential  dimensions  are  shown  in  the  sketches,  with 
the  exception  of  the  bore  of  the  armature  chamber,  which  is,  of  course, 
the  same  as  for  the  single-coil  magnet  —  4  3-16  ins.  As  the  two  magnets 
require  the  same  treatment,  varying  only  in  dimensions,  the  following 
remarks  apply  to  both: 

It  will  be  noticed  that  the  feet  of  the  machine  project  \  in.  below  the 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


J 

F. 

i 

i 

I  i 

-/- 


mi- 


t 


. 


It ^Mi 


ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE 


37 


body  and  that  there  is  a  transverse  rib  under  the  center  of  similar  depth. 
These  are  to  give  the  machine  a  floor  bearing  which  may  be  trued  up  on 
a  shaper  or  planer  without  finishing  the  whole  bottom  of  the  machine. 
The  first  operation  on  the  casting  is  chipping  off  the  numerous  fins  and 
lumps  with  which  steel  castings  are  invariably  afflicted.  An  emery  wheel 
may  be  used  for  this  purpose  around  the  outside  of  the  frame,  but  in  the 
corners  of  the  coil  spaces  a  cape  chisel  and  lots  of  muscular  exertion  will 
be  required. 

Next,  the  bearing  surfaces  are  trued  up,  and  J-in.  holes  drilled  in  the 
feet;  then  the  magnet  is  mounted  for  boring  out  the  armature  chamber 
and  the  seats  for  the  journal  yokes,  all  of  which  must  be  done  with  one 
mounting.  This  finishes  the  magnet  frame,  unless  it  is  desired  to  put  a 
terminal  block  on  the  machine  instead  of  on  the  base  and  do  away  with 


^ ix > 


FIG.  34 

the  latter.  In  this  event  four  }-in.  holes  are  to  be  drilled  in  the  top  surface 
of  the  frame  and  tapped  for  machine  screws  to  hold  the  block,  which  may 
be  2  by  6  ins.  and  ij  ins.  thick.  The  journal  yoke  and  journal  are  the 
same  as  shown  in  Fig.  29,  except  that  for  the  bipolar  magnet  the  yoke  is 
yj  ins.  long  instead  of  4§  ins. 

The  field  coils  for  the  bipolar  machine  consist  of  No.  25  single-cotton- 
covered  wire  wound  if  ins.  deep,  and  each  coil  is  2  ins.  long  parallel  to 
the  magnet  core.  The  coils  should  be  wound  in  fiber  bobbins,  as  shown 
by  Fig.  35.  The  heads  of  the  bobbin  must  be  2  ins.  apart,  and  the  body 
must  be  J  in.  wider  and  longer  than  the  magnet  core,  actual  measurement. 
Before  winding  the  coil  the  bobbin  must  be  mounted  on  a  wooden  core  of 
proper  size  to  fit  the  opening  through  the  center,  and  having  flanges  or 
heads  at  each  end  to  "back  up"  the  heads  of  the  bobbins;  one  of  these 


3 3  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

heads  is  put  on  permanently  and  the  other  is  secured  by  two  screws  so  as 
to  be  removable.  A  spindle  of  i-in.  iron  goes  through  the  center  of  the 
wooden  core  upon  which  to  mount  it  in  the  lathe  for  winding. 

When  a  coil  is  completed  bend  the  wire  back  upon  itself  near  the  end, 

tie  a  linen  thread  in  the  loop  formed,  and  secure  the  end  of  the  coil  by 

passing  the  thread  several  times  around  the  coil  and  tying  its  ends  together. 

Then  varnish  the  outside  heavily  and  bake  the  coil  at  a  low  temperature 

-  100  to  125  deg.  Fah.  —  until  the  varnish  is  hard. 

The  coils  for  the  four-polar  machine  are  i  in.  deep  and  3  ins.  long, 
of  No.  25  single-cotton-covered  wire.  The  heads  of  the  winding  bobbin 
are  3  ins.  apart.  The  instructions  for  winding  the  coils  for  the  bipolar 
iron-clad  machine  apply  to  these  also.  In  connecting  the  coils  on  the 
machine,  however,  there  is  a  difference.  On  the  bipolar  machine  the 
final  end  of  one  coil  must  be  connected  to  the  beginning  of  the  other;  on 
the  quadripolar  the  reverse  is  true.  Fig.  37  shows  diagrammatically  the 


FIG.  35 


manner  of  connecting  the  field  coils  of  the  quadripolar  machine.  It  will 
be  noticed  that  the  exciting  current  passes  around  the  cores  in  opposite 
directions.  The  connection  for  the  bipolar  machine  is  exactly  the  reverse 
of  that  shown. 

The  armature  core  of  the  four-pole  machine  has  33  slots  0.2  in.  wide 
and  }  in.  deep.  There  are  33  coils,  each  having  20  turns  of  No.  20  wire, 
4  turns  wide  and  5  turns  deep.  These  may  be  wound  directly  on  the  core, 
but  it  will  probably  be  easier  for  an  amateur  to  wind  them  in  a  little  frame, 
tie  them  at  intervals  with  thread  and  put  them  on  the  core  complete. 
The  winding  frame  will  be  exactly  like  the  one  for  the  field  coils  except  in 
size.  The  " channel"  formed  between  the  heads  must  be  J-  in.  wide  and 
7-32  in.  deep.  The  body  of  the  frame,  which  determines  the  length  and 
width  of  the  coil,  is  2\  ins.  one  way  and  2  j  ins.  the  other.  The  coils  are 
put  on  and  connected  up  as  indicated  by  the  accompanying  table. 


ONE-HALF  HORSE-POWER  MOTOR  WITH  DRUM  ARMATURE         39 


TABLE  OF  WINDING  AND  CONNECTIONS 


NUMBER  OF 
COIL 

IN  SLOTS 
NOS. 

BEGINNING  END 
GOES  TO  SEG- 
MENT NUMBER 

FINAL  END 
GOES  TO  SEG- 
MENT NO. 

I 

i  and  9 

I 

17 

2 

2   "   10 

2 

18 

3 

3     IX 

3 

J9 

4 

4     12 

4 

20 

5 

5     J3 

5 

21 

6 

6  "  14 

6 

22 

7 

7  "  I5 

7 

23 

8 

8  "  16 

8 

24 

9 

17  "  25 

17 

33 

10 

18  "  26 

18 

I 

ii 

19  "  27 

19 

2 

12 

20   "   28 

20 

3 

13 

21   "   29 

21 

4 

14 

22       30 

22 

5 

15 

23   ;  31 

23 

6 

16 

24    ;   32 

24 

7 

J7 

25   :  33 

25 

8 

18 

26  "   i 

26 

9 

19 

27   "    2 

27 

10 

20 

28  "   3 

28 

ii 

21 

29     4 

29 

12 

22 

30  "   5 

3° 

13 

23 

31  «   6 

31 

14 

24 

32     7 

32 

15 

25 

33  "   8 

33 

16 

26 

9     I7 

9 

25 

27 

10  "  18  . 

10 

26 

28 

ii  "  19 

ii 

27 

29 

12   "   20 

12 

28 

3° 

I3       21 

13 

29 

31 

14       22 

14 

3° 

32 

15       23 

15 

31 

33 

16     24 

16 

32 

FIG.  37 


40  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

The  numbers  of  the  coils  indicate  the  sequence  in  which  they  are  put 
on  the  core,  and  this  order  should  be  observed  in  order  to  secure  maximum 
symmetry  of  the  wires  across  the  heads  of  the  core.  The  numbers  of  the 
slots  and  segments  refer  to  the  diagram  shown  in  Fig.  36.  Each  figure 
applies  to  the  slot  and  segment  between  which  it  is  located. 

The  brush  quadrant  for  this  machine  is  also  different  from  that  of 
the  other  two;  instead  of  bearing  upon  the  commutator  at  diametrically 
opposite  points,  the  brushes  must  be  90  deg.  apart  —  corresponding  with 
the  relative  angular  positions  of  magnet  poles  of  different  signs.  In  the 
bipolar  iron-clad  the  "north"  and  " south"  poles  are,  of  course,  opposite 
each  other;  in  the  four-pole  machine  the  poles  directly  opposite  are  of 
the  same  sign  —  if  one  horizontal  pole  is  "nortK"  the  other  must  also  be 
"  north,"  and  the  other  two,  without  coils,  will  be  "  south." 


CHAPTER  VI 
ONE  HORSE-POWER  BIPOLAR  MOTOR  WITH  DRUM  ARMATURE 

THE  accompanying  drawings  and  description  will  enable  any  one 
with  moderate  machine-shop  facilities  to  build  a  i  horse-power  motor  to 
work  on  a  no- volt  direct-current  circuit.  Two  types  of  field  magnet  are 
given,  the  armature  and  shaft  being  the  same  in  both  cases. 

The  armature  is  4  ins.  in  diameter,  outside,  with  twenty-four  slotsr 
each  7-32  in.  wide  and  f  in.  deep.  Fig.  38  shows  the  shaft  and  a  cross- 
sectional  view  of  the  armature  core.  The  discs  are  compressed  by  two 
cast-iron  end  plates,  which  are  screwed  on  the  shaft ;  these  plates  are  J  in. 


FIG.  38 

thick  at  the  shaft,  and  taper  to  3-16  in.  thick  at  the  outer  edge,  which  is 
rounded  as  shown,  to  avoid  abrading  the  insulation  between  the  core  and 
the  windings.  The  full  list  of  armature  dimensions  is  as  follows: 

Core  Shaft 

Body.     Heads,  at  1.       m.       n.  p.  q. 

Diameter 4             2f  i           f         i  f           \ 

Axial  length    4               J  5           if         5  3!  2 

The  discs  should  have  a  shallow  key-seat  in  the  edge  of  the  central 
hole,  and  the  shaft  should  be  "correspondingly  key-seated,  and  a  spline, 
or  perfectly  straight  key,  \  in.  square,  should  be  used  to  transmit  the  move- 
ment of  the  discs  to  the  shaft.  If  this  is  done,  the  slots  in  the  periphery 

41 


42  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

of  the  discs  may  be  milled  out;  the  armature  core  must  be  dismantled 
after  the  slots  are  cut,  and  the  burr  which  is  left  by  the  milling  center 
smoothed  off.  If  the  key  and  key-seats  are  properly  fitted  the  discs  will 
go  back  on  the  shaft  in  precisely  the  position  in  which  the  slots  were  cut, 
and  the  sides  of  the  latter  will  be  smooth.  If  the  key  is  a  loose  fit,  how- 
ever, it  will  be  advisable  to  use  a  straight-edge  in  one  of  the  slots  to  insure 
perfect  accuracy  in  reassembling  the  discs.  It  is  scarcely  necessary  to 
urge  a  very  careful  and  close  fit  of  the  key  and  its  seats.  In  assembling 
the  core,  one  of  the  cast-iron  heads  should,  of  course,  be  screwed  to  place 
first;  then  put  on  a  disc  of  vulcanized  fiber,  1-16  in.  thick,  4  ins.  in  diameter, 
and  next  thread  on  the  iron  discs.  After  the  last  iron  disc  put  on  another 
fiber  disc  and  follow  with  the  end  plate  or  head  of  cast  iron,  which  will 
have  to  be  set  up  with  a  pin  wrench.  If  the  discs  are  purchased  with  the 
slots  already  stamped  out  notches  will  have  to  be  cut  in  the  fiber  end 
discs  to  correspond  with  the  armature  slots;  if  the  slots  are  to  be  milled 
the  fiber  discs  will,  of  course^  be  cut  along  with  the  iron  ones.  The  latter 


FIG.  39 


FIG.  40 


must  be  not  over  25  mils  thick  and  preferably  thinner;  care  should  be 
taken  to  get  low-carbon  annealed  steel  discs. 

Of  the  two  types  of  field  magnets  shown,  the  iron-clad  is  preferable 
from  a  constructional  standpoint,  as  the  only  operations  are  boring  out 
the  armature  chamber  and  the  seats  for  the  journal  pedestals,  and  drilling 
the  bolt  holes  for  the  latter.  Fig.  39  gives  a  plan  view  of  the  iron-clad 
magnet,  Fig.  40  an  end  view  and  Fig.  41  a  side  elevation.  The  thickness 
of  the  magnet  core  (the  portion  on  which  the  coils  are  placed)  parallel 


ONE  HORSE-POWER  BIPOLAR  MOTOR 


43 


with  the  shaft  is  4^  ins.  except  right  at  the  pole  face,  where  it  is  rounded 
down  to  4  ins. ;  this  is  necessary  in  order  to  reduce  the  flow  of  magnetism 
from  the  pole  to  the  cast-iron  end  plates  of  the  armature,  which  produces 
waste  of  energy  by  heating.  The  complete  measurements  of  the  field 
magnet  are  as  follows: 

INCHES 

A  —  Thickness  of  yoke  portion  of  magnet i  £ 

B  —  Inside  length  of  horizontal  part  of  yoke 8 

C  —  Vertical  thickness  of  magnet  core 4 J 

D  —  Distance  from  core  to  yoke 2§ 

E  —  Total  outside  width  of  magnet  frame 1 1 

F  —  Width  of  journal   foot 3 

G  —  Radius  to  which  journal  seat  is  bored 4! 

H  —  Horizontal  thickness  of  magnet  core  (see  above) 4 \ 

J   —  Length  of  journal  foot,  commutator  side 4§ 

K  —  Width  of  magnet  yoke  or  frame,  axially 8J 

L  —  Length  of  journal  foot,  pulley  side 2§ 


The  bore  of  the  pole-pieces  is  4  3-16  in.  in  diameter,  and  this  figure 
must  be  rigidly  observed  for  best  results,  as  all  the  calculations  are  based 
upon  the  resulting  length  of  air-gap.  The  above  dimensions  are  intended 

to  apply  to  a  magnet  made  of  the  best      f ^ 

grade  of  cast  iron ;  Scotch  pig  should 
be  used  if  it  is  obtainable,  and  if  not, 
then  the  very  best  grade  of  soft  iron. 
The  casting  should  be  allowed  to  re- 
main in  the  mold  until  it  is  absolutely 
cold,  care  being  taken  not  to  remove 
any  of  the  sand  from  about  the 
magnet  proper.  The  sand  can  be 
scraped  away  from  the  extreme  end 
of  the  longer  of  the  two  pedestal  feet, 
so  as  to  enable  the  molder  to  ascer- 
tain when  the  casting  is  cold.  It  is 
frequently  the  case  that  a  casting 
requires  as  much  as  two  days  to 
thoroughly  cool,  but  it  should  not  be 
disturbed  before  it  is  cold. 

Fig.  42  gives  outside  and  cross-sectional  views  of  the  journal  pedestal 
for  this  magnet;  the  two  pedestals  are  alike  in  every  particular,  and  when 
in  position  on  the  projecting  feet  of  the  field-magnet  frame  their  outer 
edges  should  be  exactly  flush  with  the  ends  of  the  feet.  The  pedestals 
are  of  iron;  the  base  is  curved  to  conform  to  the  arc  of  the  circle  to  which 
the  upper  surface  of  the  foot  is  machined,  and  is  f  in.  thick.  The  standard 
consists  of  two  ribs  at  right  angles  with  each  other,  each  f  in.  thick,  with 


FIG.  41 


44 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


their  edges  curved  as  shown.  The  box  is  of  the  ring-oiling  type,  with  a 
single  ring  hung  midway  of  the  journal;  the  bushing  is  easily  made  from 
thin  brass  tubing,  f  in.  outside  diameter,  and  with  a  very  thin  wall  (not 
over  1-32  in.),  babbitted  to  fit  the  shaft  and  having  a  slot  f  in.  wide  cut 
half  way  through  it,  midway  between  its  ends.  This  bushing  is  shown  in 
Fig.  43,  which  represents  the  bearing  for  the  other  type  of  magnet,  to  be 
presently  described.  The  bushing  is  i  J  ins.  long;  the  oil  ring  is  made  of 
brass,  one  inch  in  diameter  inside,  ij  ins.  diameter  outside,  and  \  in. 
wide  along  the  shaft.  Reference  to  the  side  views  of  the  journal  pedestal 
will  show  a  slot  in  the  upper  wall  of  the  box  portion,  through  which  the 


i--* 


FIG.  42 


oil  ring  is  inserted  before  putting  in  the  bushing.  A  cover  should  be  pro- 
vided for  this  slot  to  keep  out  dust,  etc.  The  dimensions  of  the  journal 
pedestals  are  as  follows: 

INCHES 

g  —  Length  of  base  and  journal  box 2\ 

h  —  Width  of  base 3 

j  —  Outer  diameter  of  reservoir 2 

k  —  Axial  length  of  reservoir,  outside \\ 

Internal  diameter  of  reservoir 2| 

Internal  length  of  reservoir i 

The  bore  of  the  box  portion  of  the  pedestal  must,  of  course,  be  made 
to  fit  snugly  the  outer  diameter  of  the  tubing  used  for  a  bushing,  as  the 
wall  of  the  latter  is  too  thin  to  admit  of  turning  it  down  to  fit  a  prede- 
termined bore  in  the  pedestal.  After  boring  the  pedestal  to  fit  the  bushing 
it  should  be  mounted  on  a  mandrel  and  its  base  turned  to  fit  the  circle  of 
the  foot  on  the  magnet  frame,  namely,  Q|  ins.  in  diameter.  Each  pedestal 
should  be  fastened  to  the  foot  with  two  }-in.  cap  screws. 

Fig.  44  gives  a  side  elevation  of  a  much  lighter  magnet,  which  may  be 
used  in  connection  with  the  armature  above  described,  if  the  builder  has 
sufficient  skill  and  facilities  to  do  the  machine  work  accurately.  The 
magnet  core  is  a  round  piece  of  wrought  iron,  3^  ins.  in  diameter,  with  its 


ONE  HORSE-POWER  BIPOLAR  MOTOR 


45 


O 


ends  turned  down  to  3!  ins.  diameter  for  a  distance  of  4  ins.  from  each, 
end;  the  total  length  of  the  core  is  i2\  ins.,  so  that  the  length  of  the  un- 
touched portion  will  be  4}  ins.  The  pole-pieces  are  of  cast  iron,  only  the 
very  best  possible  grade  being  suitable.  Wftere  the  core  enters  the  cast 
iron  the  latter  is  4  ins.  square,  with 
the  corners  rounded,  and  having  two 
ribs  or  flanges,  /,  /,  running  along  one 
edge;  these  continue  clear  up  to  the 
top  of  the  pole-piece,  and  are  i  in. 
thick  by  2  ins.  wide.  Fig.  45  shows  an 
end  view  of  the  magnet  frame,  and 
Fig.  46  a  plan  view.  The  hole  occu- 
pied by  the  wrought-iron  core  should 
be  cored  out  to  2  J  ins.  diameter  when 
the  casting  is  made,  and  afterward 
bored  to  a  driving  fit  of  the  end  of 
the  core. 

The  first  operation  should  be  turn- 
ing off  the  ends  of  the  core;  next, 
bore  the  holes  in  the  pole-pieces  (or, 
more  strictly  speaking,  the  yokes). 


f 

'0' 


FIG.  44 


FIG.  45 


FIG.  46 


Then  drill  a  f-in.  hole  through  the  yoke  just  below  the  lower  edge  of  the 
big  hole  and  at  right  angles  with  it,  to  accommodate  the  clamping  bolt 
shown  in  Fig.  45.  Next  drive  one  end  of  the  core  into  one  yoke  and  set 


46  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

up  the  nut  on  the  end  of  the  clamping  bolt;  then  put  on  the  other  yoke 
and  twist  it  on  the  core  until  the  four  horns  of  the  pole-pieces  are  exactly 
opposite  each  other,  tighten  up  the  second  clamping  bolt,  and  plane  off 
the  bottom  surfaces  of  both -yokes.  To  bring  the  pole  horns  into  align- 
ment, the  simplest  method  is  to  cut  out  two  heavy  blocks  of  hard  wood, 
say  3  ins.  thick  and  3^  ins.  square;  bore  a  J-in.  hole  through  the  center 
of  each  block,  run  a  J-in.  bolt,  12  ins.  long,  through  the  two  blocks,  and 
apply  them  to  each  side  of  the  pole-pieces,  the  bolt  passing  through  the 
armature  chamber  in  about  the  position  to  be  occupied  by  the  shaft.  Set 
up  the  nut  on  the  bolt  until  the  blocks  are  hard  against  all  four  pole  horns, 
and  then  tighten  up  the  clamping  bolt  in  the  foot  of  the  loose  yoke. 

After  planing  off  the  feet  of  the  frame,  bore  out  the  armature  chamber 
4  3-16  ins.  in  diameter,  and  the  seats  for  the  journal  yokes  (in  opposite 
faces  of  the  side  flanges,  /,  /),  5  ins.  in  diameter,  and  then  remove  one 
magnet  yoke  and  put  on  the  magnet  coil.  If  the  coil  is  separately  wound 
in  a  form  (which  is  preferable)  only  one  yoke  need  come  off;  if  it  is  wound 
directly  upon  the  core,  both  yokes  must  come  off,  of  course.  The  base 
of  the  machine  must  be  of  wood  or  brass.  Wood  is  better,  as,  aside  from 
its  cheapness,  it  affords  convenient  space  for  the  terminal  posts  and  fuse- 
block  of  the  machine.  The  base  should  be  15  ins.  x  18  ins.,  made  of  two 
pieces  of  hard  wood  each  ij  ins.  thick,  glued  and  screwed  together  with 
the  grains  at  right  angles.  The  longer  dimension  of  the  base  is  to  go 
parallel  with  the  shaft,  and  the  machine  should  be  so  set  as  to  allow  the 
pulley  to  overhang  the  edge  of  the  base-board. 

The  pulley  should  be  4  ins.  in  diameter  and  2  ins.  wide  on  the  face; 
the  latter  should  be  crowned.  The  pulley  should  preferably  be  keyed 
to  the  shaft,  with  a  set-screw  in  the  pulley  hub  on  top  of  the  key.  If 
only  a  set-screw  be  used  to  hold  the  pulley  on  the  shaft,  a  "flat"  must 
be  filed  on  one  side  of  the  shaft  under  the  point  of  the  set-screw. 

The  journal  box  and  yoke  for  this  magnet  is  shown  by  Fig.  43.  It 
must  be  made  of  brass  or  some  other  non-magnetic  composition.  The 
design  and  dimensions  of  the  oil  reservoir,  journal  box,  and  bushing  are 
exactly  the  same  as  those  given  for  the  journal  box  of  the  iron-clad  magnet 
above.  All  the  dimensions  are  given  in  the  following  list,  along  with 
those  of  the  magnet  just  described. 

INCHES 

A  —  Distance   between  yokes 4^ 

B  —  Thickness  of  yoke ' 4 

C  —  Radius  of  outer  curve  of  pole-piece 4 J 

D  —  Length  of  pole  horn 1 1 

E  —  Distance  from  pole  horn  to  center  of  magnet  core 3} 

F  —  Distance  from  floor  line  to  center  of  magnet  core 3! 

G  —  Width  of  foot 2| 

H  —  Width  of  slot  under  core  hole  in  yoke i  j 

]   —  Width  of  yoke 4 


ONE  HORSE-POWER  BIPOLAR  MOTOR  47 

K  —  Width  of  flange 2 

a   —  Diameter  of  curve  of  journal  yoke  ends  and  seats 5 

b  —  Vertical  width  of  journal  yoke  arms 2\ 

c   —  Length  of  machined  portion  of  yoke  arms i  \ 

d  —  Distance  from  end  of  yoke  arm  to  inner  end  of  journal  box, 

pulley  end  of  shaft 2 

d  —  Distance  from  end  of  yoke  arm  to  inner  end  of  journal  box,  com- 
mutator end  of  shaft 4 

e   —  Length  of  bushing i 

g  —  Length  of  journal  box 2 

h  —  Slot  to  let  in  the  oil  ring §xi 

j    —  Outer  diameter  of  oil  reservoir 2 

Outer  length  of  reservoir,  axially i  \ 

The  armature  core  and  field-magnet  frames  may  be  wound  for  any 
voltage  desired,  but  the  most  efficient  windings,  as  the  cores  now  stand, 
will  be  those  specified  below. 

ARMATURE   WINDING 

The  armature  core,  after  being  finally  assembled,  is  to  be  made  ready 
for  windings  by  applying  the  insulation.  Cut  out  four  discs  of  heavy 
canvas,  3  ins.  in  diameter,  with  a  f-in.  hole  in  the  center;  varnish  two  of 
them  on  one  side  with  shellac  varnish,  and  apply  them  to  the  end  plates 
of  the  armature  core,  varnished  sides  in.  The  edges  will  turn  over  to 
cover  the  outer  edges  of  the  plates,  and  will  have  to  be  slitted  at  intervals 
of  |  in.  all  around  to  prevent  bunching  up.  After  putting  on  these  varnish 
their  outer  faces,  and  one  face  of  each  of  the  remaining  canvas  discs; 
when  the  varnish  begins  to  thicken  put  on  the  two  other  discs,  one  at 
each  end,  and  apply  considerable  pressure  to  them  until  they  dry.  This 
is  best  accomplished  by  boring  a  hole  in  a  piece  of  plank,  large  enough  to 
pass  the  shaft,  and  setting  the  core  on  the  plank,  on  end,  next  putting  a 
short  piece  of  board  (6  or  8  ins.  square)  with  a  hole  in  its  center  on  the 
upper  end  of  the  armature,  and  piling  any  convenient  pieces  of  heavy 
scrap  on  the  top  board. 

Next  insulate  the  slots  with  troughs  of  oil  paper,  1-64  in.  thick,  such 
as  is  used  with  the  ordinary  office  outfit  for  copying  letters;  each  trough 
should  consist  of  two  thicknesses  of  the  oil  paper,  and  the  floor  of  the 
trough  should  be  4^  ins.  long,  so  as  to  project  a  little  beyond  the  iron  of 
the  core  and  rest  upon  the  edges  of  the  canvas  discs,  which  were  previously 
turned  over  to  cover  the  edges  of  the  end  plates. 

The  coils  may  then  be  wound  directly  in  the  slots,  each  coil  consisting 
of  20  turns  of  No.  18  double-cotton-covered  wire,  4  wide  and  5  deep. 
Each  slot  will  contain,  when  the  windings  are  complete,  half  of  each  of 
two  separate  coils.  It  will  facilitate  the  winding  and  insure  electrical 
balance  (as  nearly  as  a  core-wound  armature  can  be  balanced)  if  the 
builder  will  make  a  diagram  of  his  armature  disc,  numbering  the  slots 


48  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

from  i  to  24  successively  around  the  circumference,  as  shown  by  Fig.  47. 
Then  the  winding  will  proceed  as  follows: 


First 

2d 

3d 

4th 

5th 
6th 
7th 
8th 
Qth 
loth 
nth 
1  2th 
i3th 
1  4th 
i5th 
1  6th 
1  7th 
1  8th 
igth 

20th 
2ISt 
22d 
23d 

24th 

coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 
coil 

starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 
starts 

in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 

slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 

No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 

i, 

!3> 

17. 

5' 
9> 

21, 

3' 

'5' 

19. 

7. 

!!> 

23> 

22, 
IO, 

18, 
6, 
14, 

2, 
2O, 

8, 
16, 
4, 
24, 

12, 

ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 
ends 

in 

in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 
in 

slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 
slot 

No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 
No. 

12 
«4 

4 

1  6 

20 

8 

14 

2 

6 
[8 

22 

10 
I  I 
23 

7 
i<> 
3 
15 
9 

2  1 

5 

'7 

*3 

i 

After  winding  the  first  two  coils,  thin  strips  of  varnished  muslin  should 
be  laid  over  them,  across  each  armature  head  from  slot  to  slot,. so  that 
the  next  two  coils  will  be  insulated  from  the  first  pair;  each  successive 


FIG.  47 


FIG.  46 


pair  of  coils  should  receive  this  treatment,  and  after  the  slots  are  half 
filled  (twelve  coils  being  put  on),  a  strip  of  oil  paper  7-32  in.  wide  and 


ONE  HORSE-POWER  BIPOLAR  MOTOR  49 

4j  ins.  long  must  be  laid  in  each  slot  on  top  of  the  coil  already  in  place 
before  proceeding  to  put  on  the  coil  which  next  goes  in  that  slot. 

The  starting  end  of  each  coil  should  be  kept  leading  out  straight  from 
its  slot,  and  the  finishing  end  should  be  brought  across  the  head  and 
secured  to  the  starting  end  by  a  turn  around  it.  When  the  winding  is 
complete,  untwist  the  finishing  end  of  each  coil  from  its  starting  end,  and 
twist  it  and  the  starting  end  of  the  next  coil  to  the  right  firmly  together. 
This  will  leave  twenty-four  terminals  to  lead  out  to  the  commutator  lugs. 

Before  connecting  the  ends  to  the  commutator,  the  binding  wires 
should  be  put  on  and  the  winding  tested  for  grounds  on  the  core.  The 
binding  wires  are  put  on  in  two  bands,  and  consist  of  small  tinned-iron 
wire;  they  should  be  put  on  beginning  i  in.  from  each  end  of  the  core, 
and  making  each  band  \  in.  wide.  The  binding  wire  should  be  wound 
on  strips  of  thin  varnished  muslin  laid  around  the  core  two  layers  deep, 
and  the  bands  should  be  soldered  at  four  equidistant  points  around  the 
armature  surface,  not  all  the  way  around.  The  wire  used  should  be  not 
larger  than  No.  22  B.  W.  G.  or  No.  20  B.  S.  G. 

Unless  the  machine  is  likely  to  be  used  in  very  dusty  surroundings  it 
is  better  not  to  put  any  covering  over  the  ends  of  the  armature  after  the 
winding  is  complete.  If  the  instructions  for  insulating  each  pair  of  coils 
from  the  succeeding  pair  have  been  carefully  followed  out,  any  ordinary 
collection  of  dust  will  not  be  liable  to  cause  a  breakdown  in  the  heads. 

The  commutator  had  better  be  purchased  from  any  well-known  man- 
ufacturer of  commutators,  as  its  market  price  will  be  less  than  the  cost 
of  material  and  labor  necessary  to  make  one  properly.  It  must  have 
twenty-four  segments  and  be  not  more  than  2  ins.  long  along  the  shaft ;  the 
diameter  does  not  matter  particularly  —  take  one  of  a  stock  size  from 
the  maker.  In  connecting  up  the  coils  to  the  commutator  carry  the  ends 
previously  twisted  together  straight  out  to  the  commutator  segments. 
Fig.  48  shows  the  connections  diagrammatically.  The  slots  are  omitted 
and  each  coil  is  represented  as  having  only  one  turn  for  the  sake  of  sim- 
plicity. The  coils  are  lettered,  to  facilitate  identification  of  opposite  ends. 
The  ends  leading  straight  to  the  commutator  are  the  starting  ends;  those 
leading  around  being  the  final  ends.  The  diagram  is  not  intended  to 
show  the  relative  radial  positions  of  the  coils,  and  care  must  be  observed 
to  avoid  becoming  confused.  For  example,  coil  A  may  or  may  not  be 
under  coil  Z  at  its  starting  side;  they  are  both  in  the  same  slot,  but  it  does 
not  matter  which  is  on  top.  If  coil  A  was  the  first  one  put  on,  it  will,  of 
course,  be  in  the  bottom  of  both  of  its  slots,  and  coil  Z  will  come  on  top 
of  each  side  of  it.  The  diagram  only  shows  the  relative  angular  positions 
of  the  coils  and  the  manner  of  connecting  their  ends.  The  brushes  should 
be  of  carbon,  f  in.  thick,  and  of  a  width  J  in.  less  than  the  length  of  the 


50  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

commutator  face,  which  should  be  about  ij  ins.  The  brush-holders  may 
be  copied  from  any  standard  type  to  which  the  builder  of  this  motor  has 
access. 

The  iron-clad  magnet  requires  two  magnet  coils,  one  on  each  pole; 
for  i ic- volt  circuits  these  coils  consist  of  No.  22  single- cotton- covered  wire 
wound  2 J  ins.  deep,  each  coil  being  ij  ins.  long.  If  both  the  coils  are 
wound  in  the  same  direction  —  in  other  words,  if  they  are  precisely  alike 
as  to  the  manner  of  winding,  as  they  should  be  —  the  beginning  end  of 
one  must  be  connected  to  the  final  end  of  the  other,  the  two  remaining 
ends  being  carried  to  the  terminals  of  the  machine.  The  best  arrangement 
is  to  connect  the  two  ends  that  are  farthest  apart,  making  this  connection 
on  the  pulley  side  of  the  machine.  The  coils  should  be  wound  on  a  block, 
the  cross-section  of  which  is  of  exactly  the  same  shape  as  that  of  the  magnet 
core  at  its  largest  part,  but  which  measures  \  in.  more  in  each  direction. 
After  winding  each  coil,  tie  it  at  each  corner  with  coarse  linen  thread 
(cobbler's  thread)  and  cover  it  with  strips  of  muslin  wound  at  right  angles 
to  the  direction  of  the  wires,  and  so  put  on  as  to  have  the  edge  of  each 
convolution  of  muslin  lay  just  alongside  that  of  its  neighbor  —  touching  it 
but  not  lapping  it.  The  muslin  must  be  one  fourth  the  width  of  the  inner 
edge  of  one  side  of  the  coil,  so  that  four  turns  will  cover  one  side  evenly. 
Put  the  muslin  on  in  two  layers,  the  turns  of  the  second  layer  covering  the 
joint  between  the  turns  of  the  first  layer.  Then  wind  strips  over  the  corners 
of  the  coils,  two  layers  deep.  After  the  coil  is  covered  with  one  layer, 
varnish  the  muslin  covering  heavily  with  shellac;  when  this  is  nearly  dry, 
put  on  the  next  layer  and  the  corner  strips,  and  after  varnishing  the  whole 
set  the  coil  aside  to  dry.  Do  not  put  any  varnish  on  the  wire  itself.  Next 
cover  the  iron  cores  of  the  machine  with  a  layerof  muslin,  this  time  lapping 
the  edges  of  successive  convolutions;  varnish  the  muslin,  and  when  it  and 
the  coils  are  thoroughly  dry,  put  the  latter  on.  Unless  the  pattern  for 
the  field  magnet  has  been  very  exactly  made,  and  the  casting  is  an  un- 
usually perfect  one,  it  may  be  necessary  to  file  the  corners  of  the  pole-pieces 
slightly  to  get  the  coil  between  them  in  putting  on  the  magnet  core.  In 
filing  these  corners,  be  careful  to  round  them,  leaving  no  sharp  corners  or 
edges  whatever.  It  is  advisable  to  do  this,  even  if  it  is  not  mechanically 
necessary  for  the  introduction  of  the  coils. 

The  single-core  magnet  has  only  one  magnet  coil,  of  course.  This 
consists  of  No.  25  single-cotton-covered  wire,  wound  to  a  depth  of  ij  ins. 
and  a  length  of  4  ins.  Circular  magnet  heads  of  vulcanized  fiber  should 
be  used  to  protect  the  ends  of  the  coil,  as  the  full  voltage  of  the  machine 
exists  between  these  ends;  these  heads  should  be  J  in.  thick  and  6f  ins. 
in  diameter,  with  a  hole  to  fit  the  magnet  core  snugly  if  the  coil  is  wound 
directly  on  the  core.  If  not,  a  bobbin  should  be  made,  the  center  consisting 


ONE  HORSE-POWER  BIPOLAR  MOTOR  51 

of  a  tube  of  i-32-in.  fiber,  4^  ins.  long,  and  of  an  internal  diameter  to  go 
easily  over  the  core;  the  heads  of  the  bobbin  to  be  of  J-in.  fiber,  as  above. 
If  the  coil  is  wound  on  the  core,  the  latter  must  be  covered  with  two  layers 
of  muslin,  each  layer  varnished  with  shellac.  The  whole  must  dry  thor- 
oughly before  the  wire  is  wound  on. 

The  data  of  the  machines  are  as  follows: 

Terminal  e.  m.  f 1 10  volts 

Armature  capacity,  maximum 8.3  amp. 

Armature  capacity,  normal     7  amp. 

Magnetic  flux  per  sq.  in.  in  armature  core   .  71,800 

Revolutions  per  minute,  loaded v.  .  .  .  1,800 

Efficiency,  approximately    7°% 

An  amateur  motor  builder  will  be  wise  not  to  attempt  to  make  a  starting 
box  for  this  size  of  machine;  one  can  be  purchased  for  a  moderate  sum 
from  any  of  half  a  dozen  reputable  manufacturers,  and,  as  either  of  the 
motors  here  described  is  well  worth  the  outlay  necessary  to  insure  its 
protection  in  this  particular,  the  writer  advises  buying  the  starting  rheostat. 

If,  however,  the  reader  particularly  desires  to  make  his  own  starting 
rheostat,  the  arrangement  shown  by  Fig.  49  will  be  found  easier  to  con- 
struct than  anything  in  the  shape  of  a  wire  rheostat.  In  the  sketch,  L  is 
the  lever,  pivoted  on  a  J-in.  metal  post,  and  normally  forced  downwardly 
by  a  coil  spring  of  three  or  four  turns  (not  shown),  which  is  located  under 
the  washer,  W.  A  pin  through  the  post  secures  the  washer,  spring,  and 
lever.  H  is  the  handle;  a  wooden  handle,  such  as  coffee  grinders  are 
given,  or  a  large  porcelain  knob,  will  answer.  B  is  the  contact  brush  of 
copper,  slitted  tangentially  to  the  circles  of  the  contact  strips,  c,  c,  c,  c,  c,  c,  c\ 
these  circles  have  their  common  center,  of  course,  in  the  center  of  the  post 
on  which  L  is  pivoted.  An  end  view  of  the  brush,  B,  is  given  by  E,  showing 
the  convex  shape  given  the  under  face  of  the  brush  to  enable  it  to  pass 
smoothly  over  the  contact  strips.  The  end  of  these  should  be  beveled  to 
avoid  digging  into  the  brush. 

The  connections  are  shown  diagrammatically.  R  is  a  bank  of  five 
32  candle-power  incandescent  lamps,  rated  at  no  volts  (100  will  be  better, 
and  they  can  probably  be  readily  obtained);  C  is  the  motor  commutator; 
b,  b,  the  brushes;  F,  the  field  winding;  S,  a  double-pole  combined  switch 
and  fuse  block,  and  M  the  service  mains.  A  glance  at  the  connections 
will  show  that  the  functions  of  the  lever  L  are  to  first  connect  in  the  field, 
next  the  armature  in  series  with  one  lamp;  at  each  successive  step  a  lamp- 
is  added  in  parallel  with  the  first  one  until  all  are  in,  and  the  last  position 
of  the  lever  cuts  out  the  lamps,  leaving  the  armature  in  circuit  direct. 

The  lamps  should  be  mounted  on  the  base  with  the  lever  and  contacts, 
and  it  is  preferable,  though  not  particularly  urgent,  that  the  switch  S  be 


52 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


mounted  on  that  base  also.  The  sketch  shows  the  lever  in  the  k'off" 
position;  the  switch,  5,  should  never  be  closed,  except  when  the  lever  L 
is  in  this  position.  If  the  reader  desires  to  make  the  arrangement  auto- 
matic he  need  only  add  a  retractile  spring  to  pull  the  lever  L  to  the  "off" 


M 


FIG.  49 

position;  a  bar  of  iron  J  in.  by  J  in.  by  2  ins.  on  the  right-hand  edge  of 
the  lever,  and  a  small  magnet  connected  in  series  with  the  field,  Ft  and 
located  on  the  base  about  Mg,  in  such  a  position  that  it  will  hold  the  lever, 
by  means  of  the  bar  of  iron,  when  it  is  brought  to  the  "on"  position. 


CHAPTER  VII 
ONE  HORSE-POWER  FOUR-POLAR  MOTOR  WITH  DRUM  ARMATURE 

FOR  the  four-polar  i  horse-power  motor  here  described  only  one  type 
of  field  magnet  is  shown,  namely,  the  familiar  ring  yoke  with  radial 
magnet  poles.  This  type  combines  more  good  points  than  any  other, 
hence  the  limitation  to  the  one  type.  A  choice  is  given,  however,  between 
cast  iron  and  cast  steel.  The  armature  construction  is  the  same  for  both 
types  of  field  magnet,  the  only  difference  being  in  the  length  of  the  core 
along  the  shaft,  and,  consequently,  the  length  of  the  shaft. 


FIG. 


Fig.  50  shows  the  shaft  and  a  cross-sectional  view  of  the  armature 
core.  The  discs  are  mounted  on  a  cast-iron  drum,  d,  which  has  a  flange 
/,  and  a  hub,  h2,  at  one  end,  and  a  hub,  h,  at  the  other  end.  Fig.  51  gives 
a  transverse  cross-sectional  view  of  the  drum,  and  Fig.  52  is  a  perspective 
view,  from  the  fkngeless  end.  The  wall  of  the  drum  is  thickened  at  two 
places,  diametrically  opposite,  as  shown  in  Fig.  51.  This  is  necessary  on 
one  side  in  order  to  provide  sufficient  metal  under  the  key-seat ;  it  is  neces- 
sary on  the  opposite  side  to  obtain  a  mechanical  balance. 

The  discs  are  held  endwise  by  a  clamping  ring,  r,  which  may  be  either 
screwed  onto  the  end  of  the  drum,  J,  or  held  on  by  four  flat-headed  screws 

53 


54 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


with  large  heads.  The  discs  are  held  from  turning  by  a  key.  At  each 
end  of  the  magnetic  core  a  disc  of  fiber,  indicated  by  heavy  black  lines, 
should  be  placed.  These  discs  must  be  exactly  like  the  core  discs,  except 
that  they  are  1-16  in.  thick. 

The  core  discs  are  5^  ins.  in  diameter  and   1-40  in.   thick,  with  3- 


FIG.  51 


FIG.  52 


slots,  each  }  in.  wide  and  9-16  in.  deep.  The  slots  have  parallel  sides. 
The  discs  must  be  of  the  best  annealed  low-carbon  steel;  the  hole  in  the 
center  is  3  ins.  in  diameter,  key-seated.  The  flange,  /,  and  the  clamping- 
ring,  r,  must  have  their  outer  edges  rounded  off  to  avoid  cutting  the  insula- 
tion of  the  winding.  The  dimensions  of  the  core  drum  are  as  below: 


INCHES 

Length  of  drum,  d 4j 

Innner  diameter  of  d 2  J 

Outer  diameter  of  d 3 

Diameter  of  flange,  f,  and  ring,  r 4 

Thickness  of  flange,  f,  and  ring,  r 

Thickness  of  d  at  thickest  point 

Diameter  of  hubs,  h  and  h2 -I 

Bore  of  hubs,  h  and  h2 i 

Length  of  hub,  h I; 

Length  of  hub,  h2 I 

Length,  a,  of  disc  portion  of  core   4 

The  shaft  measurements  are  as  follows: 


At 


Diameter,  inches 
Length,  inches 


v         x 

f         I 

3         2 


The  shoulders  where  v  and  x  meet  and  where  y  and  z  meet  should  be 
slightly  rounded  off  at  the  corner  and  filleted  in  the  angle.  A  key  should 
be  used  to  fasten  each  hub  to  the  shaft,  but  the  machine  will  doubtless 
give  satisfaction  with  only  one  key,  that  one  being  in  the  hub,  h,  at  the 
pulley  end. 

Figs.  53  to  56  inclusive  show  end  and  side  views  and  cross-sections 
of  a  journal  pedestal  and  box.  The  two  bearings  are  alike  in  every  pur- 


ONE  HORSE-POWER  FOUR-POLAR  MOTOR 


55 


ticular,  and  are  made  of  cast  iron.  The  base  or  foot  is  tooled  to  conform 
to  the  circle  to  which  the  pedestal  seat,  on  the  magnet  frame,  is  machined, 
and  is  J  in.  thick.  The  standard  or  pedestal  consists  of  two  ribs  at  right 
angles  to  each  other,  \  in.  thick  and  having  curved  edges,  as  shown.  The 
box  is  of  the  ring-oiling  type,  with  a  single  ring  hung  about  midway  of 
the  journal;  the  bushing  is  easily  made  from  thin  brass  tubing,  J  in.  outside 
diameter,  and  with  a  very  thin  wail  (not  over  1-32  in.),  babbitted  to  fit 
the  shaft  and  having  a  slot  f  in.  wide  cut  half  way  through  it,  nearly  mid- 
way between  its  ends;  accurately,  slot  must  be  \  in.  nearer  one  end  than 
the  other.  The  bushing  is  2f  ins.  long;  the  oil  ring  is  made  of  brass, 
1}  ins.  in  diameter  inside,  i  11-16  ins.  diameter  outside,,  and  J  in.  wide 
along  the  shaft.  Reference  to  the  side  views  of  the  journal  pedestal  will 
show  a  slot  in  the  upper  wall  of  the  box  portion,  through  which  the  oil 
ring  is  inserted  before  putting  in  the  bushing.  A  cover  should  be  provided 
for  this  slot  to  keep  out  dust,  etc.  The  dimensions  of  the  journal  pedestals 
are  as  follows: 


B  —  Radius  of  arc,  pedestal  seat 

g  —  Length  of  circular  oil  reservoir 

i  —  Length  of  journal  box 

Bore  of  journal  box  

j  —  Diameter  of  oil  reservoir 

Internal  diameter  of  oil  reservoir 

J  —  Width  of  pedestal  foot 

k  —  Length  of  pedestal  foot 


INCHES 
Si 

.      .        2 


The  bore  of  the  box  portion  of  the  pedestal  must,  of  course,  be  made 
to  fit  snugly  the  outer  diameter  of  the  tubing  used  for  a  bushing,  as  the 


FIG.  53 


FIG.  55 


FIG.  56 


wall  of  the  latter  is  too  thin  to  admit  of  turning  it  down  to  fit  a  prede- 
termined bore  in  the  pedestal.     After  boring  the  pedestal  to  fit  the  bushing 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


FIG.  58 


ONE  HORSE-POWER  FOUR-POLAR  MOTOR 


57 


it  should  be  mounted  on  a  mandrel  and  its  base  turned  to  the  radius  B, 
of  5}  ins.,  which  is  the  same  as  the  radius  of  the  circle  of  the  foot  on  the 
magnet  frame.  Each  pedestal  should  be  fastened  to  the  foot  with  four 
J-in.  cap  screws. 

Of  the  two  field  magnets  shown,  the  cast-iron  one  will  be  found  much 
easier  to  make  because  there  is  less  tooling  to  be  done  and  iron  castings 


FIG.  59 

are  smoother  than  steel,  requiring  little  or  no  finishing  elsewhere  than  the 
pedestal  seats  and  pole  faces.  Fig.  57  shows  the  cast-iron  magnet  frame 
and  Fig.  58  the  cast-steel  frame.  Fig.  59  is  a  plan  view  of  either  frame 
and  Fig.  60  is  an  edge  view. 

The  measurements  for  the  cast-iron  magnet  are  as  follows: 


INCHES 


A  —  Bore  of  armature  chamber  ................................ 

B    —  Radius  to  which  pedestal  seat  is  bored  ...................... 

C  —  Outer  diameter  of  yoke  ring  ..............................  13 

D  —  Distance  between  parallel  inner  faces  of  yoke  ring  ...........  10 

E  —  Width  of  plane  surface  behind   coil  ,  .......................  5 

F  —  Width  of  magnet  coil  ....................................  2 

F2  —  Breadth  of  magnet  core  ..................................  4 

G  —  Distance  from  core  to  angle  of  yoke  ......  '  ...................  i 


DESIGNS  FOR  SMALL  DYNAMOS  AND   MOTORS 


H  —  Width  of  frame  foot 

H2  —  Length  of  double  foot 

J    —  Width  of  pedestal  lug  and  seat 

K  —  Length  of  pedestal  lug  commutator  side . 

L  —  Length  of  pedestal  lug  pulley  side 

k    —  Length  of  pedestal  seat 

•    M  —  Axial  width  of  magnet  yoke 


3 
5l 

3i 

3 

7 


Fig.  6 1  shows  the  cross-section  of  a  magnet  core,  from  which  it  will 
be  seen  that  the  corners  of  the  core  are  rounded  off.  The  radius  of  the 
curve  here  is  J  in.  The  only  machining  that  should  be  required  for  this 


frame  is  boring  the  armature  chamber  and  pedestal  seats  and  drilling  12 
bolt-holes.  The  frame  should  be  clamped  to  a  lathe  carriage  with  its 
_  center  true  with  the  lathe  centers,  and  the  boring 
done  at  one  setting  by  means  of  a  boring  bar  and 
•  tool.  Both  pedestal  seats  should  be  cut  before  the 
frame  is  moved  from  its  original  position. 

The  magnet  must  be  made  of  the  very  best  grade 
of  iron  obtainable;  use  Scotch  pig  if  possible.     It 
should  be  allowed  to  remain  in  the  sand  until  it  is 
cold,  care  being  taken  not  to  remove  any  of  the  sand  around  the  magnet 


ONE  HORSE-POWER  FOUR-POLAR  MOTOR 


59 


portion  until  the  casting  is  ready  to  come  out.  The  longer  of  the  two 
lugs  might  advantageously  be  placed  uppermost  in  putting  the  pattern  in 
the  sand,  and  after  the  casting  has  been  cooling  for  24  hours  the  sand  may 
be  scraped  away  from  the  end  of  this  lug  so  that  its  temperature  may  be 
noted. 

The  steel  field  magnet  is  much  preferable  if  the  reader  has  the  skill 
and  facilities  to  make  it  properly.  The  difference  from  the  cast-iron 
magnet  consists  in  making  the  magnet  cores  round  instead  of  oblong,  and 
putting  on  pole-shoes.  The  length  of  the  machine  is  thereby  reduced 
one  inch,  but  all  the  transverse  measurements  remain  unchanged.  The 
magnet  ends  are  machined,  exactly  as  in  the  case  of  the  cast-iron  frame, 
but  the  bore,  A2,  is  greater,  namely,  6J  ins. 


K — e — -» 


FIG.  62 


FIG.  63 


FIG.  64 


The  pole-pieces  are  made  in  one  piece,  called  a  polar-bushing,  like 
Fig.  62,  and  this  had  better  be  done  before  the  magnet  is  bored  out.  This 
bushing  is  a  simple  cylinder  of  cast  iron  with  four  openings  in  its  wall, 
equidistant  from  each  other.  Fig.  63  shows  the  exact  shape  of  each  of 
these  openings.  The  measurements  of  the  bushing  are  these: 


INCHES 

Si 


A  —  Bore  of  bushing,  finished 

A2  —  Diameter  of  bushing,  finished 

a2  —  Length  of  bushing,  finished 3^ 

b    —  Length  of  openings  in  wall    3 

c    —  Radius  of  curve,  side  of  opening 4 

e    —  Maximum   width  of  opening , . . .  if 


60  DESIGNS  FOR  SMALL  DYNAMOS  AND   MOTORS 

The  casting  for  this  bushing  should  be  about  3!  ins.  long,  6|  ins.  in 
diameter,  and  5!  ins.  bore  in  the  rough.  After  it  has  been  turned  down 
to  the  finished  diameter,  mount  the  magnet  frame  and  bore  out  its  polar 
circle  to  such  a  size  that  the  bushing  is  a  snug  fit  —  not  quite  a  driving 
fit,  but  tight  enough  to  prevent  turning  by  hand.  Then  insert  the  bushing 
so  that  the  openings  in  its  sides  come  half  way  between  the  magnet  cores, 
and  scribe  the  outlines  of  two  opposite  cores  on  its  surface. 

Remove  the  bushing  and  set  a  steel  pin  at  each  extremity  of  each 
ellipse  scribed  on  the  surface.  Then  put  the  bushing  back  and  bore  it 
out  for  the  armature  chamber.  The  pins  will  take  up  against  the  edges 
of  the  magnet  cores  and  prevent  the  bushing  from  turning.  After  boring 
it  out,  turn  off  the  ends  of  the  bushing  so  as  to  leave  the  connecting  webs 
from  pole-piece  to  pole-piece  J  in.  thick. 

The  objection  to  this  magnet  is  the  difficulty  of  fitting  the  bushing  to 
the  magnet  with  sufficient  accuracy  to  make  good  magnetic  contact  and 
still  leave  it  loose  enough  to  permit  removal  without  breaking  the  thin 
connecting  webs.  This  could  be  obviated  by  bolting  the  pole-pieces  to 
the  ends  of  the  magnet  cores  by  means  of  long,  slender  machine  screws, 
put  in  from  the  outside  of  the  yoke  through  holes  in  the  centers  of  the 
magnet  cores.  Then  the  connecting  webs  could  be  sawed  out  entirely, 
leaving  each  pole-shoe  independent  of  the  others.  This  construction  is 
also  magnetically  preferable,  and  if  the  builder  has  means  for  drilling  a 
J-in.  hole  from  the  outside  of  the  ring  to  the  end  of  the  magnet  core  (a 
distance  of  3^  ins.),  the  pole-shoes  should  be  held  on  this  way. 

With  the  steel  magnet  the  following  measurements  must  be  substituted 
for  those  previously  given  : 

INCHES 

F  —  Diameter  of  magnet  core  ...................................  2f 

M  —  Width  of  magnet  yoke  ....................................  6 

a  —  Length  of  disc  part  of  core  ................................  3 

Length  of  drum,  d  ............................................  3  J 

.........  2§ 


Outer  diameter  of  drum,  d 
Inner  diameter  of  drum,  d 


The  four  field  coils  for  the  cast-iron  magnet  frame  described  in  the 
preceding  chapter  are  of  No.  21  single-cotton-covered  magnet  wire.  The 
depth  of  the  winding  must  be  i\  ins.,  as  nearly  as  possible,  and  the  length 
along  the  core  should  be  2  ins.  Careful  and  close  winding  should  give 
40  layers  of  wire,  with  58  turns  to  a  layer.  Whatever  number  of  turns 
the  reader  may  obtain,  that  number  must  be  precisely  the  same  in  all  four 
coils.  In  order  to  attain  uniformity  the  coils  should  be  wound  upon  a 
frame  and  the  turns  religiously  counted. 

It  will  be  found  advantageous  to  tie  a  knot  in  the  starting  end  of  each 
coil  before  taping  it,  so  that  it  may  be  identified  afterward.  The  coils 


ONE  HORSE-POWER  FOUR-POLAR  MOTOR 


61 


must  be  connected  up  as  shown  by  the  diagram,  Fig.  64,  so  that  the  starting 
end  of  one  connects  to  the  finishing  end  of  its  neighbor.  .This  presupposes 
that  all  four  are  wound  in  the  same  direction,  as  they  should  be. 

The  coils  for  the  cast-steel  magnet  are  of  No.  24  single-cotton-covered 
wire,  ij  ins.  deep  and  if  ins.  long.  Good  winding  will  enable  the  reader 
to  put  on  50  layers  of  wire  and  75  turns  to  a  layer.  As  in  the  previous 
case,  however,  the  depth  in  inches  is  the  essential  point,  though  it  is  ad- 
vantageous to  get  as  many  layers  in  that  depth  as  possible.  The  coils 
are,  of  course,  wound,  insulated,  and  connected  up  exactly  like  the  oblong 
coils  of  the  cast-iron  frame. 

The  armature  core  for  either  of  the  magnet  frames  will  contain  32 
coils;  each  coil  consists  of  No.  21  double-cotton-covered  wire,  wound  5 
turns  wide  by  4  layers  deep.  Each  slot^  contains  one  side  of  each  of 
two  coils,  so  that  the  cross-section  of  the 
winding  in  a  slot  will  be  as  in  Fig.  65,  except 
that  the  wire  will  lie  closer  together  than  the 
sketch  indicates.  All  armature  coils  should  be 
wound  on  a  forming  bobbin  so  that  they  will 
all  be  exactly  alike.  Fig.  66  shows  what  the 
essential  dimensions  should  be.  The  width  of 
the  hollow  of  the  coil  is  the  same  for  both  arma-  FlG>  65 

ture  cores.  As  the  armature  core  to  be  used  with  the  steel  magnet  is  an 
inch  shorter  than  the  other  one,  the  coils  for  this  core  must  be  an  inch 
shorter;  hence  the  two  dimensions  for  coil  lengths. 

Fig.  67  is  a  winding  diagram  and  shows  the  first  four  coils  in  position. 
The  coils  are  indicated  by  a  single  line  across  the  head  and  dots  in  the 
slots  for  simplicity.  The  builder  should  note  that  the  left-hand  side  of 
each  coil  is  in  the  bottom  of  the  slot  and  the  right-hand  side  is  on  top;  this 
should  be  true  of  every  coil.  The  starting  ends  should  be  knotted  for 
identification,  and  all  the  knotted  ends  should  occupy  the  same  relative 
position  on  the  core.  For  smoothness  of  finished  heads  the  coils  should 
be  put  on  the  core  in  the  following  order: 


Coils  i,  2,  3, 
Coils  5,  6,  7, 
Coils  9,  10,  n, 
Coils  13,  14,  15, 
Coils  17,  18,  19, 
Coils  21,  22,  23, 
Coils  25,  26,  27, 
Coils  29,  30,  31, 


4  in  Slots  i-  9,  9-17, 
8  in  Slots  2-10,  10-18, 
12  in  Slots  3-11,  11-19, 
1 6  in  Slots  4-12,  12-20, 
20  in  Slots  5-13,  13-21, 
24  in  Slots  6-14,  14-22, 
28  in  Slots  7-15,  15-23, 
32  in  Slots  8-16,  16-24, 


17-25,25-1 
18-26,  26-2 
19-27,  27-3 
20-28,  28-4 
21-29,  29-5 
22-30,  30-6 

23-3! >3J-7 
24-32,32-8 


If  put  in  properly,  the  coils  will  give  a  regular  sequence  of  knotted  ends 
and  straight  ends,  one  each  projecting  from  each  slot.     The  connections 


62 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


to  the  commutator  are  then  simple.  Carry  all  the  knotted  ends  straight 
out  to  the  commutator,  and  the  straight  ends  one  segment  less  than  a 
quarter  circle  backwards  from  their  corresponding  knotted  ends.  Thus, 


X 


INSIDE  WIDTH 
— 4— " 


FIG.  66 


31 


30 


29 


28 


13      ,7      16 

FIG.  67 


the  knotted  end  from  slot  No.  i  goes  to  commutator  segment  No.  i  (see 
Fig.  68),  and  so  on,  all  the  way  around.  Then  the  straight  ends  go  to 
the  commutator  as  follows: 


From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 
From 


Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 
Slot  No. 


1  to  Segment 

2  to  Segment 

3  to  Segment 

4  to  Segment 

5  to  Segment 

6  to  Segment 

7  to  Segment 

8  to  Segment 

9  to  Segment 
10  to  Segment 
-ii  to  Segment 

12  to  Segment 

13  to  Segment 

14  to  Segment 

15  to  Segment 

1 6  to  Segment 

17  to  Segment 

1 8  to  Segment 

19  to  Segment 

20  to  Segment 

21  to  Segment 

22  to  Segment 

23  to  Segment 

24  to  Segment 


No.  26 
No.  27 
No.  28 
No.  29 
No.  30 
No.  31 
No.  32 
No.  i 
No.  2 
No.  3 
No.  4 
No.  5 
No.  6 
No.  7 
No.  8 
No.  9 
No.  10 
No.  ii 
No.  12 
No.  13 
No.  14 
No.  15 
No.  16 
No.  17 


ONE  HORSE-POWER  FOUR-POLAR  MOTOR  63 

From  Slot  No.  25  to  Segment  No.  18 
From  Slot  No.  26  to  Segment  No.  19 
From  Slot  No.  27  to  Segment  No.  20 
From  Slot  No.  28  to  Segment  No.  21 
From  Slot  No.  29  to  Segment  No.  22 
From  Slot  No.  30  to  Segment  No.  23 
From  Slot  No.  31  to  Segment  No.  24 
From  Slot  No.  32  to  Segment  No.  25 

The  commutator  must  have  32  segments,  as  indicated  by  Fig.  68, 
and  should  be  purchased  already  built  for  assured  satisfaction.  The 
brush  surface  of  the  commutator  must  be  ij  ins.  long  at  least,  so  that 
carbon  brushes  i  in.  wide  and  \  in.  thick  can  be  used.  The  diameter 
of  the  barrel  of  the  commutator  should  not  be  less  than  3,  and  preferably 
4  ins.  The  brush-holders  and  yoke  may  be  copied  advantageously  from 
any  of  the  standard  machines  now  on  the  market.  Four  brushes  must 
be  used,  and  the  two  diametrically  opposite  are  connected  together,  as 
shown  by  Fig.  69. 

The  windings  just  described  are  for  machines  to  work  on  a  no-ii5-volt 
circuit.  If  windings  for  220-230  volts  are  desired  the  armature  coils 
should  be  of  No.  25  wire,  each  coil  five  layers  deep  and  eight  turns  wide, 
making  ten  layers  of  wire  per  slot.  The  field  coils  of  the  cast-iron  magnet 
must  be  of  No.  24  s.c.c.  wire,  wound  to  the  dimensions  specified  above, 


TERMINAL 


FIG.  68 


FIG.  69 


namely,  ij  ins.  deep  and  2  ins.  long.     The  coils  for  the  cast-steel  magnet 
will  be  of  No.  27  wire  wound  to  a  depth  of  ij  ins.  and  a  length  if  ins. 

The  principal  magnetic  and  electrical  data  of  the  two  machines  are 
as  follows: 


64  DESIGNS  FOR  SMALL  DYNAMOS  AND   MOTORS 

II5-VOLT   MOTOR 

Cast  iron.  Cast  steel. 

Resistance  armature  winding i  ohm  0.9 

Normal  armature  currents 9  amp.  9  amp. 

Approximate  speed   1600  1600 

Density  in  field  cores    48,000  93,000 

Density  in  air  gap 27,500  37)5°° 

Efficiency,  assuming  10  perl 

cent  friction  and  windage} '  '  7°  Per  ™  Per 

As  in  the  preceding  case,  it  is  by  far  preferable  to  buy  a  starting  box 
from  one  of  the  standard  rheotsat  manufacturers.  If  the  reader  insists 
upon  having  a  home-made  one,  however,  the  arrangement  shown  by  Fig. 
49  and  described  on  pages  51  and  52  will  answer. 


CHAPTER  VIII 

TWO  HORSE-POWER  FOUR-POLAR  MOTOR  WITH  TWO-PATH  DRUM 

ARMATURE 

FOR  this  motor,  as  in  the  preceding  design,  only  one  type  of  field  magnet 
is  shown,  namely,  the  familiar  ring  yoke  with  radial  magnet  poles;  a 
choice  is  given  between  cast-iron  and  cast-steel  field  magnets.  The  arma- 
ture construction  is  identical  for  both  types  of  magnet,  there  being  a 
difference  only  in  the  length  of  the  armature  and  shaft. 

Fig.  70  shows  the  shaft  and  a  cross-sectional  view  of  the  armature 
core.  The  discs  are  mounted  on  a  cast-iron  drum,  d,  which  has  a  flange, 


FIG.  70 

/,  and  a  hub,  h2,  at  one  end,  and  a  hub,  k,  at  the  other  end.  Fig.  71  gives 
a  transverse  cross-sectional  view  of  the  drum,  and  Fig.  72  is  a  perspective 
view,  from  the  flangeless  end.  The  wall  of  the  drum  is  thickened  at  two 
places,  diametrically  opposite,  as  shown  in  Fig.  71.  This  is  necessary  on 
one  side  in  order  to  provide  sufficient  metal  under  the  key-seat;  it  is  neces- 
sary on  the  opposite  side  to  obtain  a  mechanical  balance. 

The  discs  are  held  endwise  by  a  clamping  ring,  r,  which  may  be  either 
screwed  onto  the  end  of  the  drum,  J,  or  held  on  by  four  flat-headed  screws 
with  large  heads.  The  discs  are  held  from  turning  by  a  key.  At  each 
end  of  the  magnetic  core  a  disc  of  fiber,  indicated  by  heavy  black  lines, 

65 


66 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


should  be  placed.     These  discs  must  be  exactly  like  the  iron  discs,  except 
that  they  are  1-16  in.  thick. 

The  steel  core  discs  are  6J  ins.  outside  diameter  and  1-40  in.  thick, 
with  43  slots,  each  \  in.  wide  and  9-16  in.  deep.  The  slots  have  parallel 
sides.  The  discs  must  be  of  the  best  charcoal  iron;  the  hole  in  the  center 
is  3!  ins.  in  diameter,  key-seated.  The  flange,  /,  and  the  clamping  ring,  r, 
must  have  their  outer  edges  rounded  off  to  avoid  cutting  the  insulation  of 
the  winding.  The  dimensions  of  the  core  drum  are  as  below : 

Length  of  drum,  d 5T^ 

Inner  diameter  of  d 3 

Outer  diameter  of  d 3§ 

Diameter  of  flange,  f,  and  ring,  r 5! 

Thickness  of  flange,  f,  and  ring,  r f-s 

Thickness  of  d  at  thickest  point | 

Diameter  of  hubs,  h  and  h2 2 

Bore  of  hubs,  h  and  h2 i 

Length   of  hub,   h i 

Length  of  hub,  h2 i 

Length  pf  a,  of  disc  portion  of  core 4 

The  shaft  measurements  are  as  follows: 


At  v 

Diameter,  inches   f 

Length,  inches 3! 


z 

I 

7i 


The  shoulders  where  v  and  x  meet  and  where  y  and  z  meet  should  be 
slightly  rounded  off  at  the  corner  and  filleted  in  the  angle.     A  key  should 

be  used  to  fasten  each  hub  to  the 
shaft,  but  the  machine  will  doubt- 
less give  satisfaction  with  only  one 
key,  that  one  being  in  the  hub,  hr 
at  the  pulley  end.  The  hub,  h, 
must  be  exactly  \  in.  from  the 
shoulder  on  the  shaft. 

Figs.  73  to  76,  inclusive,  show  end 
and  side  views  and  cross-sections 
of  a  journal  pedestal  and  box.  The 

two  bearings  are  alike  in  every  particular,  and  are  made  of  cast  iron. 
The  base  or  foot  is  tooled  to  conform  to  the  circle  to  which  the  pedestal 
seat,  on  the  magnet  frame,  is  machined,  and  is  f  in.  thick.  The  standard 
or  pedestal  consists  of  two  ribs  at  right  angles  to  each  other,  f  in.  thick 
and  having  curved  edges,  as  shown.  The  box  is  of  the  ring-oiling  type, 
with  a  single  ring  hung  about  midway  of  the  journal;  the  bushing  is 
easily  made  from  thin  brass  tubing,  i  in.  outside  diameter,  and  with  a 
very  thin  wall  (not  over  1-32  in.),  babbitted  to  fit  the  shaft  and  having 


FIG.  71 


FIG.  72 


TWO  HORSE-POWER  FOUR-POLAR  MOTOR 


67 


a  slot  7-16  in.  wide  cut  half  way  through  it,  nearly  midway  between  its 
ends;  accurately,  the  slot  must  be  \  in.  nearer  one  end  than  the  other. 
The  bushing  is  3!  ins.  long;  the  oil  ring  is  made  of  brass,  2  ins.  in 
diameter  inside,  2\  ins.  diameter  outside,  and  f  in.  wide  along  the  shaft. 
Reference  to  the  side  views  of  the  journal  pedestal  will  show  a  slot  in  the 


FIG.  75 


upper  wall  of  the  box  portion,  through  which  the  oil  ring  is  inserted 
before  putting  in  the  bushing.  A  cover  should  be  provided  for  this  slot 
to  keep  out  dust,  etc.  The  dimensions  of  the  journal  pedestals  are  as 
follows : 

INCHES 

B  —  Radius  of  arc,  pedestal  seat 6 

g  —  Length  of  circular  oil  reservoir 2 

i  —  Length  of  journal  box 3! 

Bore  of  journal  box i 

j  —  Diameter  of  oil  reservoir 2| 

Internal  diameter  of  oil  reservoir z\ 

J  —  Width  of  pedestal  foot 3§ 

k  —  Length  of  pedestal  foot 3§ 

The  bore  of  the  box  portion  of  the  pedestal  must,  of  course,  be  made 
to  fit  snugly  the  outer  diameter  of  the  tubing  used  for  a  bushing,  as  the 
wall  of  the  latter  is  too  thin  to  admit  of  turning  it  down  to  fit  a  prede- 
termined bore  in  the  pedestal.  After  boring  the  pedestal  to  fit  the  bushing 
it  should  be  mounted  on  a  mandrel  and  its  base  turned  to  the  radius  B, 
of  6  ins.,  which  is  the  same  as  the  radius  of  the  circle  of  the  foot  on  the 
magnet  frame.  Each  pedestal  should  be  fastened  to  the  foot  with  four 
5-i6-in.  cap  screws. 

Of  the  two  field  magnets  shown,  the  cast-iron  machine  will  be  found 
easier  to  make  because  there  is  less  tooling  to  be  done  and  iron  castings 
are  smoother  than  steel,  requiring  little  or  no  finishing  elsewhere  than 


68 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


the  pedestal  seats  and  pole  faces.  Fig.  77  shows  the  cast-iron  magnet 
frame  and  Fig.  78  the  cast-steel  frame.  Fig.  79  is  a  plan  view  of  either 
frame  and  Fig.  80  is  an  edge  view. 


FIG.  77 


The  measurements  for  the  cast-iron  magnet  are  as  follows: 


INCHES 
7 


A  —  Bore  of  armature  chamber 

B  —  Radius  to  which  pedestal  seat  is  bored  ..... 

C  —  Outer  diameter  of  yoke  ring  ...............................  15! 

D  —  Distance  between  parallel  inner  faces  of  yoke  ring  ..........  12 

E  —  Width  of  plane  surface  behind  coil  ........................     6 

F  —  Width  of  magnet  core  ....................................     3 

F2  —  Breadth  of  magnet  core  ..................................     4  J 

G  —  Distance  from  core  to  angle  of  yoke  ......  ...................      i  J 

H  —  Width  of  frame  foot  ......................................     2\ 

H2  —  Length  of  double  foot  ....................................     5 

J  —  Width  of  pedestal  lug  and  seat  ............................  3§ 

K  —  Length  of  pedestal  lug,  commutator  side  ....................  6| 

L  —  Length  of  pedestal  lug,  pulley  side  ..........................  3! 

k  —  Length  of  pedestal  seat  ..................................  3! 

M  —  Axial  width  of  magnet  yoke  ...................  .  ..........     8r75 

Fig.  8  1  shows  the  cross-section  of  a  magnet  core,  from  which  it  will 
be  seen  that  the  corners  of  the  core  are  rounded  off.     The  radius  of  the 


TWO  HORSE-POWER  FOUR-POLAR  MOTOR 


69 


curve  here  is  0.3  in.  The  only  machining  that  should  be  required  for 
this  frame  is  boring  the  armature  chamber  and  pedestal  seats  and  drilling 
12  >bolt-holes.  The  frame  should  be  clamped  to  a  lathe  carriage  with 


FIG.  78 


its  center  true  with  the  lathe  centers,  and  the  boring  done  at  one  setting 
by  means  of  a  boring  bar  and  tool.  Both  pedestal  seats  should  be  cut 
before  the  frame  is  moved  from  its  original  position. 

The  magnet  must  be  made  of  the  very  best  grade  of  iron  obtainable; 
use  Scotch  pig  if  possible.  It  should  be  allowed  to  remain  in  the  .sand 
until  it  is  cold,  care  being  taken  not  to  remove  any  of  the  sand  around 
the  magnet  portion  until  the  casting  is  ready  to  come  out.  The  longer 
of  the  two  lugs  might  advantageously  be  placed  uppermost  in  putting  the 
pattern  in  the  sand,  and  after  the  casting  has  been  cooling  for  24  hours 
the  sand  may  be  scraped  away  from  the  end  of  this  lug  so  that  its  temper- 
ature may  be  noted. 

The  cast-steel  field  magnet  is  much  preferable,  if  the  reader  has  the 
skill  and  facilities  to  make  it  properly.  The  difference  from  the  cast-iron 
magnet  consists  in  making  the  magnet  cores  round  instead  of  oblong, 
and  putting  on  pole-shoes.  The  length  of  the  machine  is  thereby  reduced 
ij  ins.,  but  all  the  transverse  measurements  remain  unchanged.  The 


jo  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

magnet  ends  are  machined  exactly  as  in  the  case  of  the  cast-iron  frame,, 
but  the  bore,  A2,  is  greater,  namely,  7^  ins. 

The  pole-pieces  are  made  in  one  piece,  called  a  polar-bushing,  like 
Fig.  82,  and  this  had  better  be  done  before  the  magnet  is  bored  out.  This 
bushing  is  a  simple  cylinder  of  cast  iron  with  four  openings  in  its  wall, 
equidistant  from  each  other.  Fig.  83  shows  the  exact  shape  of  each  of 


K— • 


these  openings.     The  measurements  of  the  bushing  are  these: 


A2  —  Diameter  of  bushing,  finished 
A  —  Bore  of  bushing,  finished 
a2  —  Length  of  bushing,  finished  ............ 

b  —  Length  of  openings  in  walls 

c  —  Radius  of  curve,  side  of  opening 

e  —  Maximum  width  of  opening 


INCHES' 


7l 


The  casting  for  this  bushing  should  be  about  4  ins.  long,  7}  ins.  in 
diameter,  and  6J  ins.  bore,  in  the  rough.  After  it  has  been  turned  down 
to  the  finished  diameter,  mount  the  magnet  frame  and  bore  out  its  polar 
circle  to  such  a  size  that  the  bushing  is  a  snug  fit  —  not  quite  a  driving 
fit,  but  tight  enough  to  prevent  turning  by  hand.  Then  insert  the  bushing 


TWO  HORSE-POWER  FOUR-POLAR  MOTOR  71 

so  that  the  openings  in  its  sides  come  half  way  between  the  magnet  cores, 
and  scribe  the  outlines  of  two  opposite  cores  on  its  surface. 

Remove  the  bushing  and  set  a  steel  pin  at  each  extremity  of  each 
ellipse  scribed  on  the  surface.  Then  put  the  bushing  back  and  bore  it 
out  for  the  armature  chamber.  The  pins  will  take  up  against  the  edges 
of  the  magnet  cores  and  prevent  the  bushing  from  turning.  After  boring 


FIG.  80 

it  out,  turn  off  the  ends  of  the  bushing  so  as  to  leave  the  connecting  webs 
from  pole-piece  to  pole-piece  J  in.  thick,  measured  axially. 

The  objection  to  this  magnet  is  the  difficulty  of  fitting  the  bushing 
to  the  magnet  with  sufficient  accuracy  to  make  good  magnetic  contact 
and  still  leave  it  loose  enough  to  permit  removal 
without  breaking  the  thin  connecting  webs.  This 
could  be  obviated  by  bolting  the  pole-pieces  to  the 
ends  of  the  magnet  cores  by  means  of  long,  slender 
machine  screws,  put  in  from  the  outside  of  the 
yoke  through  holes  in  the  centers  of  the  magnet 
cores.  Then  the  connecting  webs  could  be  sawed 

out   entirely,  leaving  each  pole-shoe  independent '  of  the  others.     This 
construction  is  also   magnetically   preferable,    and    if    the    builder   has 


f 

1 

f 

<_  p.  * 

72  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

means  for  drilling  J-in.  holes  through  the  magnet  cores  from  the  outside 
of  the  yoke  ring  to  the  inside  of  the  bushing  (a  distance  of  4|  ins.),  the 
pole-shoes  should  be  held  on  this  way. 

With  the  steel  magnet  the  following  measurements  must  be  substituted 
for  those  previously  given: 

INCHES 

F  —  Diameter  of  magnet  core 2  J 

M  —  Width  of  magnet  yoke 7T35 

a  —  Length  of  disc  part  of  core 3! 

Length  of  drum ,  d 3|| 

Length  of  part  y ,  of  shaft 7! 

This  is  to  say,  the  machine  must  be  exactly  ij  ins.  shorter,  axially. 

The  four  field  coils  for  the  cast-iron  magnet  frame  are  of  No.  22  single- 
cotton-covered  magnet  wire.  The  depth  of  the  winding  must  be  ij  ins., 
as  nearly  as  possible,  and  the  length  along  the  core  should  be  2\  ins. 
Careful  and  close  winding  should  give  50  layers  of  wire,  with  70  turns  to 
a  layer.  Whatever  number  of  turns  the  reader  may  obtain,  that  number 
must  be  precisely  the  same  in  all  four  coils.  In  order  to  attain  uniformity 
the  coils  should  be  wound  upon  a  frame  and  the  turns  religiously  counted. 

It  will  be  found  advantageous  to  tie  a  knot  in  the  starting  end  of  each 


FIG.  82 


FIG.  84 


coil  before  taping  it  so  that  it  may  be  identified  afterward.  The  coils 
must  be  connected  up  as  shown  by  the  diagram,  Fig.  84,  so  that  the  starting 
end  of  one  connects  to  the  finishing  end  of  its  neighbor.  This  presupposes 
that  all  four  are  wound  in  the  same  direction,  as  they  should  be. 


TWO  HORSEPOWER  FOUR-POLAR  MOTOR 


73 


The  coils  for  the  cast-steel  magnet  are  of  No.  23  single-cotton-covered 
wire;  ij  ins.  deep  and  2  ins.  long.  Good  winding  will  enable  the  reader 
to  put  on  56  layers  of  wire  and  70  turns  to  a  layer.  As  in  the  previous 
case,  however,  the  depth  in  inches  is  the  essential  point,  though  it  is  ad- 
vantageous to  get  as  many  layers  in  .that  depth  as  possible.  The  coils 
are,  of  course,  wound,  insulated,  and  connected  up  exactly  like  the  oblong 
coils  of  the  cast-iron  frame. 


FIG.  85 


FIG.  88 


The  armature  core  for  either  of  the  magnet  frames  will  contain  43 
coils;  each  coil  consists  of  No.  16  double-cotton-covered  wire,  wound  three 
turns  wide  by  three  layers  deep.  Each  slot  contains  one  side  of  each  of 
two  coils,  so  that  the  cross-section  of  the  winding  in  a  slot  will  be  as  in 
Fig.  85. 


FIG.  86 


FIG.  87 


All  armature  coils  should  be  wound  on  a  forming  bobbin  so  that  they 
will  all  be  exactly  alike.  Fig.  86  shows  what  the  essential  dimensions 
should  be.  The  width  of  the  hollow  of  the  coil  is  the  same  for  both  arma- 
ture cores.  As  the  armature  core  to  be  used  with  the  steel  magnet  is  ij  ins. 


74  DESIG'NS  FOR  SMALL  DYNAMOS  AND  MOTORS 

shorter  than  the  other  one,  the  coils  for  this  core  must  be  correspondingly 
shorter;  hence  the  two  dimensions  for  coil  lengths. 

Fig.  87  is  a  winding  diagram  and  shows  four  coils  in  position.  The 
coils  are  indicated  by  single  lines  across  the  head  and  dots  in  the  slots  for 
simplicity.  The  builder  should  note  that  the  left-hand  side  of  each  coil 
is  in  the  bottom  of  the  slot  and  the  right-hand  side  is  on  top;  this  should 
be  true  of  every  coil,  but  it  is  not  imperative.  The  machine  will  work 
just  as  well  if  half  of  the  coils  are  put  on  with  both  sides  bottom  and  the 
other  half  on  top  of  them,  but  the  job  will  not  be  so  neat  on  the  armature 
heads.  The  spacing  or  pitch  of  the  coils  must  be  exactly  as  indicated  — 
10  slots  in  between  the  two  sides  of  each  coil. 

The  starting  ends  should  be  knotted  for  identification,  and  all  the 
knotted  ends  should  occupy  the  same  relative  position  on  the  core.  If 
put  in  properly,  the  coils  will  give  a  regular  sequence  of  knotted 
ends  and  straight  ends,  one  each  projecting  from  each  slot.  The  con- 
nections to  the  commutator  are  then  simple.  Carry  all  the  knotted  ends 
straight  out  to  the  commutator,  and  each  straight  end  to  a  segment  22 
bars  from  the  one  to  which  the  knotted  end  is  connected.  Fig.  88 
represents  one  coil  connected,  and  shows  that  there  are  21  segments 
between  the  two  to  which  the  coil  ends  go,  reckoning  around  that  side  of 
the  commutator  nearest  the  coil  itself.  This  spacing  must  be  observed 
throughout. 

The  commutator  must  have  43  segments  and  should  be  purchased 
already  built  for  assured  satisfaction.  The  brush  surface  of  the  commu- 
tator must  be  ij  ins.  long,  at  least,  so  that  carbon  brushes  ij  ins.  wide 
and  |  in.  thick  can  be  used.  The  diameter  of  the  barrel  of  the  commu- 
tator should  not  be  less  than  4,  and  preferably  5  ins.  The  brush-holders 
and  yoke  may  be  copied  advantageously  from  any  of  the  standard  machines 
now  on  the  market.  Only  two  brushes  are  to  be  used,  and  these  set 
precisely  a  quarter  of  a  circle  apart,  reckoning  around  the  barrel  of  the 
commutator. 

The  windings  just  described  are  for  machines  to  work  on  a  101-115- 
volt  circuit.  If  windings  for  220-230  volts  are  desired  the  armature  coils 
should  be  of  No.  19  wire,  each  coil  5  layers  deep  and  4  turns  wide, 
making  10  layers  of  wire  per  slot.  The  field  coils  for  the  cast-iron  magnet 
must  be  of  No.  26  s.c.c.  wire,  wound  to  the  dimensions  specified  above, 
namely,  ij  ins.  deep  and  2\  ins.  long.  The  coils  for  the  cast-steel  magnet 
will  be  of  No.  27  wire  wound  to  a  depth  of  ij  ins.  and  a  length  of  2  ins. 
For  5oo-volt  service  use  No.  23  double-cotton-covered  wire  on  the  arma- 
ture, six  turns  wide  and  seven  layers  deep,  per  coil;  84  wires  per  slot. 
On  the  cast-iron  magnet  use  No.  29  double-covered  wire  and  on  the  steel 
magnet  No.  30. 


TWO  HORSE-POWER  FOUR-POLAR  MOTOR  75 

The  principal  magnetic  and  electrical  data  of  the  two  machines  are 
below: 

II5-VOLT   MOTOR 

Cast  iron  Cast  steel 

Resistance  armature  winding  .................  T  ohm 


Density  in  air-gap 


CHAPTER  IX 
THREE  HORSE-POWER  MOTOR 

THE  motor  design  which  forms  the  subject  of  this  chapter,  although 
somewhat  similar  to  those  described  in  Chapters  VII  and  VIII,  differs 
considerably  in  the  constructional  details  of  the  magnet.  Here  a  cast-iron 
ring  and  wrought-iron  cores  are  employed  with  a  view  to  simplifying  the 
work  as  far  as  possible  without  sacrificing  the  efficiency  of  the  machine, 
and  also  without  making  it  unduly  heavy.  The  cast-iron  ring  is  preferably 
made  in  a  single  piece  and  the  wrought-iron  cores  are  turned  to  a  very 
slight  taper  and  drawn  into  holes  in  the  yoke  ring  by  means  of  a  bolt  and 
heavy  washer  from  the  outside.  Unless  the  builder  has  excellent  machine- 
shop  facilities,  however,  and  is  an  expert  machinist,  this  construction  will 
be  found  rather  difficult,  as  it  is  necessary  to  have  a  perfect  fit  between 
the  taper  of  the  magnet  core  and  that  of  the  hole  in  which  it  is  seated. 

As  an  alternative  the  magnet  frame  can  be  cast  in  two  pieces,  the 
division  being  along  the  line,  x,  Fig.  91.  If  the  motor  is  built  in  this  way, 
each  half  must  be  chucked  and  the  joint  faced  off  fairly  smooth,  although 
it  is  not  necessary  to  have  a  perfect  joint,  as  no  magnetic  lines  of  force 
cross  the  break.  After  truing  up  the  abutting  faces  of  each  half  of  the 
magnet  ring  the  two  halves  should  be  clamped  together  with  1-32  in.  of 
cardboard  in  between  them  and  four  straight  holes  bored  for  the  reception 
of  the  field-magnet  cores. 

Fig.  89  is  a  semi-sectional  elevation  of  the  field  magnet  complete 
without  the  journal  pedestals;  a  field-magnet  core  is  shown  by  Fig.  90. 
The  cast-iron  pole-pieces  must  be  accurately  fitted  to  the  ends  of  the 
cores  and  pinned  permanently  in  place  with  iron  pins.  The  magnet  ring 
and  pole-pieces  should  be  of  the  best  grade  of  pig  iron  obtainable.  The 
magnet  cores  should  be  made  of  Norway  wrought  iron  if  obtainable;  if 
not,  of  the  mildest  machinery  steel.  The  corners  of  the  pole-pieces  should 
be  heavily  rounded  so  that  no  sharp  edges  are  left.  The  length  of  the 
pole-piece  parallel  with  the  shaft  is  the  same  as  its  width  at  right  angles 
to  this  dimension.  The  outside  diameter  of  the  magnet  ring  is  2oJ  ins. 

76 


THREE  HORSE-POWER  MOTOR 


77 


FIG.  89 

The  extreme  breadth  of  the  ring  parallel  with  the  shaft  is  8  ins     The 
other  dimensions  are  as  below: 


A  —  Bore  of  armature  chamber.  . 

B  —  Axial  length  of  pole-face 

-  Width  of  pole-piece,  tip  to  tip^  'in'  a'  straight  'line.' .'  .' .' .' .' .' .' .'  \\\     \ 


INCHES 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


FIG.  91 


3 


D  —  Radius  to  which  pedestal  seat  is  cut 

E  —  Thickness  of  yoke  ring 

F  —  Distance   between  ribs 7 

G  —  Width  of  plane  surface  back  of  magnet  coil ,  .  .  . 4$ 

H  —  Height,  base  line  to  armature  center. 12 

O  —  Axial  length  of   pedestal  seat 4 

P  —  Straight-line  width  of  pedestal  (width  of  pedestal  seat  is  the  same)  7 

Q  —  Length  of  pedestal  foot,  commutator  side 7 


THREE  HORSE-POWER  MOTOR 


79 


The  dimensions  of  the  magnet  core  (Fig. 
90)  are  as  follows: 


At      y       m     p 

Diameter,  ins 2^     3! 

Length,  ins 2       3 


FIG.  90 


Fig.  91  is  an  edge  view  of  the  field-magnet  frame,  including  one  journal 
pedestal  shown  in  perspective  and  the  other  in  cross-section.  After  fitting 
the  magnet  cores  into  place  in  the  ring,  the  pole-pieces  should  be  bored 
and  the  pedestal  seats  cut,  at  one  setting  of  the  frame.  Fig.  92  is  a  cross- 
section  of  the  armature  core, 
showing  the  details  of  construc- 
tion. The  discs  are  mounted 
on  a  cast-iron  drum,  which  is 
provided  with  a  flange  head  and 
a  hub,  J,  at  one  end,  the  other 
end  being  open.  The  discs  are 
clamped  in  place  by  a  cast- 
iron  ring  which  is  provided 
with  a  hub,  /,  similar  to  that 
at  the  other  end  of  the  drum, 
and  drawn  to  place  by  means 
of  six  J-in.  bolts  passing  through 
holes  in  the  clamping  ring  and 
tapping  into  the  end  wall  of  the  cast-iron  drum.  The  center  lines  of  two 
of  these  bolts  are  indicated  by  b  b.  The  cast-iron  drum  should  have  a 
key-seat  cut  in  it  so  that  the  discs  may  be  positively  driven. 

Both  the  hub  on  the  end  of  the  drum  and  that  on  the  clamping  ring 
should  be  keyed  to  the  shaft  so  that  there  will  be  no  opportunity  for  dis- 
placement. At  each  end  of  the  core  structure  a  disc  of  fiber  1-16  in.  thick 
should  be  provided,  as  indicated  by  the  heavy  black  lines  in  the  engraving. 
These  discs  must  be  toothed  exactly  like  the  core  discs  so- that  the  ends  of 
the  magnetic  core  will  be  entirely  covered.  The  iron  core  discs  are  7  j  ins. 
in  diameter,  with  a  central  hole  4!  ins.  in  diameter,  and  47  slots  \  in. 
wide  and  f  in.  deep;  the  slots  have  parallel  sides.  The  discs  must  be  of 
the  best  grade  of  low  carbon  steel,  1-40  in.  thick.  The  dimensions  of  the 
armature  core  structure  are  as  follows: 


FIG.  92 


INCHES 


B  —  Internal  length  of  drum 

I  —  Length  of  hub  clear  through . 

Bore  of  this  hub 

J  —  Length  of  hub  clear  through .  .  . 

Bore  of  this   hub.  . 


8o 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


K  —  Diameter  of  hubs 
L  —  Internal  diameter  of  core  drum 
M  —  Outer  diameter  of  core  drum 
N  —  Diameter  of  flange  and  clamping  ring 
Thickness  of  flange  and  clamping  ring 


4 
4! 


The  two  journal  pedestals  are  exactly  alike  and  made  of  ordinary 
cast  iron.  The  base  must  be  turned  accurately  to  conform  to  the  circle 
to  which  the  pedestal  seat  on  the  magnet  frame  is  machined.  The  stand- 
ard, or  pedestal,  is  an  open  frame  of  J-in.  metal;  the  box  is  of  the  ring- 
oiling  type,  with  a  single  ring  hung  exactly  midway  of  the  journal.  Fig.  93 
is  a  transverse  cross-section  of  the  pedestal  and  box.  The  box  is  bushed; 
the  bushing  may  consist  of  a  brass  casting  turned  to  shape,  or  it  may  be 

made  by  babbitting  a  piece  of  thin  brass  tub- 
ing, the  outer  diameter  of  which  is  a  snug  fit 
in  the  box.  The  oil  slot  across  the  center  of 
the  box  must  be  provided  with  a  suitable  cov- 
ering to  exclude  dust.  Each  pedestal  should 
be  bolted  to  the  magnet  frame  with  two  f-in. 
cap  screws.  The  pedestal  and  box  measure- 
ments are  below: 

INCHES 

P  —  Widest  part  of  standard  .......  .  ......  7 

R  —  Axial  length  of  oil  well  ................  2\ 

S  —  Inner  length  of  oil  well  ...  .............  2 

T  —  Inner  width  of  oil  well  ................  3 

t  —  Radius  line  to  indicate  origin  of  circle  .  .  i  \ 

U  —  Outside  diameter  of  box  ..............  i\ 

V  —  Inside  diameter  of  box  ......  ,  .........  i  \ 

W  —  Outside  length  of  box  ................  4 

Y  —  Length  of  bushing  ....................  3! 

Bore  of  bushing  ......................  i 

Z  —  Pr°jection  °f  box  beyond  oil-well  wall  .  .  .  \\ 

Diameter  of  oil  ring  ...................  2  J 

Bore  of  oil  ring  .......................  1  1 

FIG.  93  Width  of  oil  ring  ......................       f 


u 


=J 


A  bearing  must  be  turned  on  the  outside  of  the  inner  end  of  the  pedestal 
on  the  commutator  side  of  the  machine,  as  indicated  in  Fig.  91,  -to  accom- 
modate the  brush-holder  yoke,  which  may  be  copied  from  any  of  the 
standard  makes.  Only  two  sets  of  brushes  are  required,  each  set  com- 
prising two  carbon  brushes  f  in.  thick  and  ij  ins.  wide;  the  two  sets  must 
touch  the  commutator  exactly  90°  (nf  segments)  apart,  center  to  center. 
The  commutator  must  have  47  segments,  and  must  measure  3  ins.  along 
the  shaft,  extreme  length.  The  commutator  core  must  be  bored  to  fit  the 
portion,  c,  of  the  shaft,  and  key-seated  to  correspond.  The  diameter  of 
the  barrel  should  be  not  less  than  4  ins.,  and  the  diameter  measured  at 
the  connecting  lugs  must  not  exceed  6J  ins.  The  brush  surface,  measured 


THREE  HORSE-POWER  MOTOR 


8l 


parallel  with  the  shaft,  must  be  2j  ins.  long.  It  will  be  best  to  buy  the 
commutator  complete  from  one  of  the  several  makers  of  this  class  of 
apparatus. 

Fig.  94  is  the  armature  shaft.     The  key-seats  are  all  f  wide  and  3-16 
deep.     The  dimensions  of  the  shaft  are  below: 


Diameter,  inches 
Length,  inches    . 


Total 
j      Length 


5r7<r       3rV 


The  field-magnet  coils  may  be  wound  directly  on  the  cores 
or  on  bobbins  made  of  thin  vulcanized  fiber.  If  they  are 
wound  directly  on  the  cores,  the  latter  must  be  wrapped  first 
with  three  layers  of  unbleached  cottons  and  painted  with 
shellac  varnish,  two  circular  coil  heads  of  hard  fiber  being 
first  fitted  to  the  large  part  of  each  core.  The  coils  consist 
of  No.  22  single-cotton-covered  wire,  wound  to  a  depth  of 
|  in.,  exactly.  The  exact  number  of  turns  is  immaterial, 
except  4:hat  all  four  coils  must  contain  the  same  number  of 
turns,  and  as  many  turns  should  be  put  on  as  can  be  got  in 
the  space  available.  With  careful  winding,  the  builder 
should  get  2,565  turns  in  each  coil.  For  a  230-volt  motor 
use  No.  25  single-cotton-covered  wire,  and  for  500  volts  use 
No.  28  double-cotton-covered,  wound  to  the  depth  specified. 
Should  the  reader  prefer  to  wind  the  coils  in  bobbins,  the 
magnet  core  need  not  be  wrapped,  of  course.  After  each 
coil  is  completed,  secure  the  outer  end  and  cover  the  outside 
layer  with  unbleached  cottons  two  layers  deep,  heavily  var- 
nished. Fig.  95  indicates  how  the  field  coils  should  be  con- 
nected up. 

The  armature  coils  of  the  ii5-volt  machine  are  of  No. 
13  double-cotton-covered  wire,  each  coil  containing  8  turns. 
The  winding  must  be  2  wires  wide  and  4  layers  deep  per 
coil,  so  that  when  the  coils  are  in  place  there  will  be  16 
wires  in  each  slot  —  2  wide  and  8  deep,  as  shown  in  Fig.  96. 
There  are  47  coils,  connected  up  wave-fashion.  In  wind- 
ing the  coils  it  will  be  advisable  to  bend  a  hook  in  each 
starting  end  and  leave  the  final  ends  straight.  The  armature 
coils  must  be  wound  in  a  former  so  that  the  outline  of  the 
opening  through  each  coil  is  a  square  measuring  4|  ins.  on 
each  side.  The  ends  should  lead  out  from  two  corners, 
and  each  coil  must  be  wrapped  carefully  and  firmly  with 


82 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


two  layers  of  German  linen  tape,  each  layer  being  painted  with  shellac 
varnish.  The  slots  in  the  armature  core  should  be  provided  with  insu- 
lating troughs  of  press  board  1-64  in.  thick. 

Put  the  coils  on  the  armature  all  the  same  way  —  bent  ends  to  the 
left  and  straight  ends  to  the  right,  facing  the  commutator.  There  must 
be  twelve  teeth  between  the  two  slots  in  which  any  given  coil  is  placed, 
and  there  must  be  22  commutator  segments  between  the  two  to  which  the 
terminals  of  any  given  coil  are  connected,  as  indicated  by  Fig.  97.  It  will 
be  found  best  to  first  put  on  12  coils  in  regular  right-handed  rotation, 


FIG.  95 


FIG.  97 


pressing  the  ends  down  closely  where  they  lap,  and  slipping  a  bit  of  thin 
oiled  paper  between  the  crossings.  This  will  put  one  layer  of  coils  in 
24  of  the  slots.  Then  put  coils  in  the  23  vacant  slots  in  the  same  fashion; 
there  will  then  be  46  half  filled  slots  and  one  filled. 

Continue  the  second  layer  of  coils  right  along  from  the  24th  coil,  fol- 
lowing the  same  plan  as  before.  At  the  finish  there  will  be  a  bent  end 
and  a  straight  end  projecting  from  each  slot.  Carry  the  bent  ends  n  or 
12  segments  to  the  left,  around  the  commutator,  and  put  them  all  in  the 
segment  slots.  Then  take  any  one  of  the  straight  ends,  find  the  bent -end 


THREE  HORSE-POWER  MOTOR  83 

which  is  the  other  terminal  of  its  coil,  and  connect  the  straight  end,  as 
shown  in  Fig.  97,  with  22  segments  between  it  and  its  mate.  The  other 
straight  ends  may  be  put  in  in  regular  order  without  tracing,  if  the  coils 
have  been  put  on  the  core  properly  and  the  bent  ends  in  the  commutator 
lugs  in  strict  sequence. 

If  it  is  desired  to  build  the  machine  for  230  volts,  wind  the  armature 
with  No.  16  double-cotton-covered  wire,  putting  15  turns  in  each  coil — 
3  wide  and  5  deep  —  so  that  each  slot  will  contain  30  wires,  3  wide  and 
10  deep.  For  500  volts,  use  No.  19  wire,  putting  28  turns  in  each  coil 
—  4  wide  and  7  deep  • —  so  that  each  slot  will  contain  56  wires,  4  wide 
and  14  deep.  The  principal  technical  data  for  the  ii5-volt  machine  are 
given  below: 

Revolutions  per  minute 1,320 

Armature  resistance,  warm 0.4  ohm 

Armature  current,  normal 22 

Armature  and  brush  drop,  volts  about 9 

Per  cent  regulation  about 8% 

Flux  density  in  air-gap 30,000 

Flux  density  in  magnet  cores 93,ooo 

Flux  density  in  magnet  yoke 48,000 

Leakage  coefficient 1.3 

Resistance  of  field  winding,  ohms 169 

Exciting  current,  amperes 0.68 

Approximate  efficiency,  allowing   5   per  cent   for   friction   and 

windage 80% 

The  starting  box  should  be  purchased  from  any  of  the  standard  rheostat 
builders;  a  satisfactory  home-made  one  of  this  size  is  rarely  produced. 


CHAPTER  X 
DIRECT-CURRENT  no-VOLT  FAN  MOTOR 

THE  construction  of  the  direct-current  fan  motor  described  in  this 
chapter  is  easily  within  the  ability  of  any  one  at  all  experienced  in  the  use 


WALL  %' THICK 


FIG.  99 


FIG. 


of  machine  tools.     The  motor  is  of  the  bipolar  iron-clad  type;  the  field 
magnet  having  the  form  and  dimensions  shown  by  Fig.  102.     Fig.  98  is 

84 


DIRECT-CURRENT  no-VOLT  FAN  MOTOR  85 

an  axial  cross-section  of  the  motor  frame  taken  vertically.  It  is  intended 
that  the  magnet  proper  shall  be  of  cast  steel  set  into  a  thin  cast-iron  shell, 
the  front  cap  of  which  is  integral  with  the  shell,  as  indicated  by  Fig.  98; 
but  if  the  builder  should  prefer,  the  entire  structure  may  be  made  a  single 
casting  of  steel.  The  first  construction  requires  somewhat  more  machin- 
ing, as  it  will  be  necessary  to  turn  up  the  exterior  of  the  field  magnet  and 
bore  out  the  cast-iron  shell  so  that  the  two  will  fit  snugly  together;  but  the 
result  will  be  a  very  much  better  looking  machine  than  if  the  field-magnet 
structure  were  wholly  of  cast  steel.  There  is  only  a  single  bearing,  the 
shell  of  which  is  cast  integral  with  the  motor  casing,  as  indicated  in  Fig.  98, 
and  this  is  provided  with  a  grease  cup  of  the  ordinary  gravity- feeding 


FIG.  100 

type.     A  cross-section  of  the  cup  is  included  in  Fig.  98,  and  a  dimensioned 
drawing  of  it  is  given  by  Fig.  99. 

The  rear  cap  of  the  motor  case,  a  sectional  elevation  of  which  is 
shown  in  Fig.  98,  is  detachable,  and  is  provided  with  a  recess  extension 
near  the  center  to  accommodate  the  commutator.  The  brush- holders, 
which  are  of  the  ordinary  tubular  type,  are  mounted  in  insulating  bushings 
in  opposite  sides  of  this  extension.  This  end  cap  is  intended  to  be  of 
cast  iron  no  matter  which  way  the  field  magnet  is  constructed.  It  is 
secured  in  place  by  means  of  nuts  which  thread  on  four  machine  screws 
that  pass  completely  through  the  field  magnet.  These  four  screws  also 
serve  to  secure  the  fan  guard  to  the  opposite  side  of  the  case,  and  in  the 
event  that  the  field  magnet  proper  is  made  of  cast  steel  and  the  case  of 


86 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


cast  iron,  the  same  screws  .serve  to  hold  the  magnet  in  the  case,  as  indicated 
in  Fig.  98  and  Fig.  100,  which  show  this  construction.  The  photograph 
shows  the  field-magnet  casing  mounted  on  a  trunnion  pedestal,  but  of 


course  the  builder  can  use  any  form  of  mounting  he  may  prefer.  This  is 
about  as  simple,  however,  as  any  that  an  amateur  can  construct  that  will 
provide  both  vertical  and  horizontal  adjustment.  The  trunnion  yoke, 


FIG.  102 


shown  in  Fig.  100,  is  a  separate  casting  with  a  stem  fitting  into  a  hole  in 
the  pedestal,  which  enables  the  motor  to  be  swung  around  about  a  vertical 
axis,  while  the  trunnions  provide  for  adjustment  up  and  down  about  a 
horizontal  axis. 


DIRECT-CURRENT  no-VOLT  FAN  MOTOR  87 

The  armature  core  is  of  the  ordinary  drum  type  provided  with  1 2  holes 
for  the  winding,  the  holes  being  located  so  that  the  outer  edges  are  1-16  in. 
below  the  edge  of  the  armature  core,  as  indicated  in  Fig.  104,  which  shows 
the  condition  of  an  armature  disc  before  the  core  is  assembled.  After 
assembling  the  discs  on  the  shaft  the  thin  webs  between  the  winding  holes 
and  the  periphery  of  the  disc  must  be  cut  away,  preferably  with  a  milling 
tool,  but  allowably  with  a  hack-saw  and  file,  leaving  the  discs  as  indicated 
by  Fig.  105.  The  holes  for  the  winding  are  f  in.  in  diameter.  Fig.  101 
is  a  cross-section  of  the  complete  core  with  the  shaft  and  commutator. 
The  brass  drum  on  which  the  core  discs  are  mounted  is  open  at  the  end 
opposite  from  the  commutator  to  allow  the  bearing  shell  on  the  motor 
frame  to  project  into  the  core.  There  is  no  bearing  beyond  the  commu- 
tator. Fig.  103  is  a  cross-section  of  the  brush-holder  with  its  insulating 
bushing. 

The  armature  winding  consists  of  12  coils  of  No.  33  double-silk-covered 
magnet  wire,  each  coil  containing  185  turns.  A  winding  diagram  may 


tf  diarru 


FIG.  103 


FIG.  104 


FIG.  105 


be  made  by  drawing  an  armature  disc  and  numbering  the  slots  successively. 
The  winding  should  proceed  as  follows:  First  wind  a  coil  in  slots  i  and  6, 
twisting  the  terminals  together  lightly  near  slot  i.  Then  turn  the  armature 
core  through  half  a  revolution  and  wind  a  coil  in  slots  7  and  12,  twisting 
the  terminals  together  near  slot  7.  The  next  two  coils  should  preferably 
come  in  slots  9  and  2,  and  3  and  8;  the  next  two  in  slots  5  and  10,  and 
ii  and  4.  This  will  complete  half  the  armature  winding.  The  seventh 
coil  goes  in  slots  10  and  5  on  top  of  the  coil  previously  wound  in  those 
slots,  but  the  terminals  are  twisted  together  at  the  opposite  side  of  the 
coil  near  slot  10.  The  eighth  coil  goes  in  slots  4  and  n;  the  ninth  coil 
goes  in  slots  2  and  9 ;  the  tenth  coil  goes  in  slots  8  and  3 ;  the  eleventh  coil 
goes  in  slots  12  and  7,  and  the  twelfth  coil  goes  in  slots  6  and  i.  The 
coil  terminals  in  each  case  should  be  twisted  together  near  the.  first-named 
slot  of  each  pair. 

In  winding  the  coils,  care  should  be  taken  to  preserve  identification  of 
the  starting  and  finishing  terminals  of  each  coil.  The  best  plan  is  to  tie 
.a  knot  in  the  starting  terminals  and  then  leave  the  finishing  terminals 


88 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


straight.  When  all  the  coils  are  in  place  untwist  the  12  pairs  of  terminals 
and  connect  the  coils  together  as  follows:  Twist  the  finishing  end  from 
slot  i  to  the  starting  end  from  slot  2;  finishing  end  from  slot  2  to  starting 

end  from  slot  3,  and  so  on  all  the  way  around 
the  armature.  Then  carry  the  twisted  terminals 
out  to  the  commutator,  the  pair  from  slots  i 
and  2  going  to  segment  No.  i,  and  the  pair  from 
slots  2  and  3  going  to  segment  No.  2,  and  the 
pair  from  slots  3  and  4  going  to  segment  No.  3, 
and  so  on  all  the  way  around.  The  terminals 
of  the  coils  cannot  be  pulled  through  straight 
out  to  the  commutator  but  must  be  laid  flat 
along  the  head  of  the  armature  winding  and 
bound  into  place  by  means  of  strings  as  illus- 
trated in  Fig.  107,  which  was  made  from  the 
photograph  of  the  complete  armature.  This 
precaution  is  necessary  in  order  to  prevent  the 
edge  of  the  recess  in  the  removable  cap  from 
chafing  the  leads  running  to  the  commutator. 

The  commutator  has  12  segments,  and  is 
preferably  of  the  construction  illustrated  in  Fig. 
101,  but  the  reader  is  strongly  advised  to  pur- 
chase a  commutator  from  any  one  of  the 
various  manufacturers  rather  than  to  attempt 
to  construct  it.  The  winding  of  the  armature 
across  the  heads  must  be  compressed  until  it 
measures  not  more  than  2f  ins.  along  the 
shaft.  The  field-magnet  winding  consists  of  two  coils  of  No.  25  single- 
cotton-covered  magnet  wire  wound  into  the  ordinary  rectangular  outline 
and  then  taped  and  bent  to  the  form  shown  in  Fig.  108.  Each  coil  must 


FIG.  107 


FIG.  108 


contain  30  layers  of  wire  and  each  layer  must  have  44  turns,  making 
1320  turns  per  coil. 

The  machine  is  designed  for  two  speeds  and  for  no- volt  direct- current 


DIRECT-CURRENT  no-VOLT  FAN  MOTOR 


89 


supply.  With  the  field-magnet  coils  connected  in  parallel  it  will  run  at 
the  maximum  speed,  and  with  the  coils  connected  in  series  it  will  run  at  the 
lower  speed.  The  magnet  coils  are  connected  in  series  with  the  armature 
irrespective  of  their  relation  with  each  other.  A  switch  should  be  provided 
in  the  base  of  the  motor  for  the  purpose  of  cutting  the  fan  in  and  out  of 
circuit,  and  changing  the  relation  between  the  field  coil  connections.  A 
diagram  of  the  switch  is  shown  by  Fig.  106.  The  details  of  its  construction 
may  be  worked  out  to  suit  the 
individual  ideas  of  the  builder,  the 
only  essential  features  being  that 
it  shall  be  mounted  on  a  non- 
combustible  base,  preferably  of 
slate  or  porcelain,  with  the  metal 
parts  so  disposed  that  they  cannot 
possibly  come  in  contact  with  the 
pedestal  base.  The  connections 
between  the  field-magnet  coils  and 
the  switch  in  the  base  are  prefer- 
ably established  by  means  of  or- 
dinary lamp  cords  led  through 
holes  in  the  end  cap  and  in  the 
pedestal  base.  Each  of  these 
holes  should  be  insulated  with  a 
substantial  fiber  bushing.  A 
double- pole  snap  switch  should 
be  inserted  between  the  motor  and 
the  supply  circuit. 

Fig.  109  shows  the  complete  motor  with  the  fan  and  guard,  but  the 
reader  is  advised  to  purchase  both  fan  and  guard  from  any  dealer  in 
electrical  supplies;  the  design  of  a  propeller  fan  is  not  a  sufficiently  simple 
matter  to  justify  an  amateur  in  attempting  it,  and  the  same  is  true  of  the 
fan  guard,  although  to  a  lesser  degree.  The  motor  should  drive  a  i2-in. 
four- blade  fan  at  1600  revolutions  per  minute,  if  supplied  with  direct 
current  at  no  volts  potential. 


FIG.  109 


CHAPTER  XI 
THREE  HORSE-POWER  LAUNCH  MOTOR 

THE  engravings  in  this  chapter  show  the  salient  features  of  a  3-horse- 
power  multipolar  motor  designed  particularly  for  driving  the  screw  pro- 
peller of  a  small  pleasure  boat,  say  14  to  16  ft.  long.  The  motor  is  intended 
to  take  about  60  amperes  at  full  load  and  to  run  at  full  speed,  with  full 
load,  when  supplied  with  40  volts  at  its  terminals.  This  means  that  20 


FIG.  no 

cells  of  storage  battery  are  required.     Speed  control  is  to  be  effected  by 
grouping  the  battery  cells  for  different  voltages. 

The  field-magnet  structure,  which  is  shown  by  Fig.  1 10,  is  of  cast  steel, 
with  six  radial  poles,  the  cross-section  of  each  of  which  is  of  the  shape 
and  dimensions  shown  by  Fig.  112.  The  poles  have  slots  cored  in  them 

90 


THREE  HORSE-POWER  LAUNCH  MOTOR 


9r 


in  the  process  of  casting,  if  ins.  wide,  and  extending  from  within  \  in. 
of  the  pole  face  clear  back  to  the  circle  of  the  yoke  ring,  and  passing,  of 
course,  clear  through  the  poles  axially.  The  object  in  coring  out  these 
slots  is  mainly  to  reduce  the  weight  of  the  machine, 
although  an  incidental  advantage  in  the  distribution 
of  magnetic  flux  in  the  air-gap  also  results.  The 
yoke  ring  is  of  the  short  barrel  type,  the  contour  of 
its  cross-section  being  perfectly  rectangular,  as  indi- 
cated in  Fig.  in.  The  edges  of  the  yoke  ring  must 
be  trued  up  at  the  same  time  that  the  pole  faces  are 
bored  out,  and  a  shallow  recess  turned  up  on  the  out- 
side of  the  yoke  for  a 'distance  of  \  in.  from  each 
edge,  as  shown  in  Fig.  in.  The  object  of  this  is 
to  provide  a  seat  for  each  of  the  end  caps  perfectly 
concentric  with  the  bore  of  the  pole  faces.  The 
motor  rests  on  two  bracket  feet  cast  integral  with  the 
yoke  ring,  as  indicated  in  Fig.  no.  In  mounting 
the  machine  in  a  boat  it  is  contemplated  that  these 
brackets  will  rest  on  small  wooden  sills  parallel  with 
the  shaft  of  the  machine,  and  bolted  to  the  framing 
of  the  boat. 

The  armature  core,  core  drum  and  shaft  are 
illustrated  by  Fig.  113,  which  is  almost  self-explana- 
tory. The  core  drum,  d,  is  of  cast  iron,  with  a  hub 
and  head  at  one  end,  and  the  armature  discs,  a,  are 
clamped  in  place  by  a  clamping  plate,  c,  at  the  other  end,  similar  to  the 
head  of  the  core  drum.  The  clamping  plate  is  drawn  into  place  by 
means  of  four  bolts  extending  through  it  and  tapping  into  the  head  of 
the  core  drum.  It  is  centered  by  a  circular  rib  fitting  into 
a  recess  in  the  interior  of  the  open  end  of  the  drum.  Both 
the  core  drum  head  and  the  clamping  plate  carry  circu- 
lar projections  or  barrels,  b  6,  for  the  purpose  of  sup- 
porting the  armature  winding,  which  is  of  the  straight- 
out  type.  The  armature  discs  should  be  keyed  to  the 
core  drum,  a  very  small  key  sufficing  for  this  purpose, 
as  the  discs  must  be  very  tightly  compressed  by  the  clamping  ring, 
and  this  will  transmit  considerable  torque  from  them  to  the  shaft.  The 
hub  of  the  armature  core  drum  must,  of  course,  be  keyed  to  the  shaft, 
and  it  is  preferable  to  also  key  the  hub  of  the  clamping  plate,  c, 
to  the  shaft,  in  order  to  avoid  any  twisting  stress  in  the  body  of 
the  core  drum.  The  armature  discs  must  have  46  slots  11-32  in.  wide 
and  i  1-16  ins.  deep,  the  slots  being  simply  rectangular,  as  shown 


FIG.  in 


FIG.  112 


g 2  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

in   Fig.    116,   which  is  a  cross-section  of  a   single   slot   and   the   wires 
within  it. 

The  armature  core  discs  are  10  13-16  ins.  in  diameter,  and  the  hole 
through  the  center  is  6-J-  ins.  in  diameter.  The  length  of  the  armature  core 
parallel  with  the  shaft  when  compressed  into  permanent  shape  must  be 
precisely  3^  ins.  The  outer  diameter  of  the  drum  must,  of  course,  fit  the 
central  hole  of  the  armature  disc,  and  its  length,  parallel  with  the  shaft, 
is  3}  ins.  The  inner  diameter  of  the  drum  is  5}  ins.  The  maximum 
diameter  of  the  coil-supporting  barrels,  b  b,  is  8f  ins.,  this  diameter  being 
next  to  the  core  discs.  The  diameter  of  the  barrels  at  their  outer  edges 
is  8|  ins.,  and  their  face  measurement,  parallel  to  the  shaft,  is  2  ins.  The 
thickness  of  the  clamping  plate,  c,  is  f  in.,  and  the  thickness  of  the  drum 
head  is  the  same.  The  thickness  of  the  coil-supporting  barrels,  b  b,  tapers 


FIG.  113 

from  J  in.  maximum  to  f  in.  at  the  edges.  The  hubs  of  both  the  core  drum 
and  the  clamping  plate  taper  from  3  ins.  to  2^  ins.  in  diameter,  and  are 
2  ins.  in  length  measured  clear  through.  The  bore  of  the  hub,  h,  is  i \  ins., 
and  it  is  counterbored  to  a  depth  of  \  in.  and  a  diameter  of  ij  ins.  The 
object  of  this  counterbore  is  merely  to  have  a  true  face  for  the  shoulder  of 
the  shaft  to  butt  against  without  involving  the  work  of  machining  the  entire 
inner  surface  of  the  drum  head.  The  clamping  plate,  c,  it  will  be  noticed, 
is  provided  with  a  projecting  ridge  fitting  into  a  counterbore  or  recess  in 
the  open  end  of  the  drum.  This  ridge  need  not  be  more  than  J  in.  deep, 
its  function  being  merely  to  center  the  clamping  plate.  The  dimensions 
of  the  various  parts  of  the  shaft  are  as  follows: 


Diameter,  ins l| 

Length,  ins .7 


THREE  HORSE-POWER  LAUNCH  MOTOR 


93 


x  The  shaft  is  intended  to  be  coupled  to  the  propeller  shaft  by  means  of 
a  plain  flange  coupling. 

The  journal  boxes  are  cast  integral  with  the  enclosing  caps  of  the  field 
magnet.  Figs.  114  and  115  are  face  views  and  cross-sections  of  these 
caps.  It  will  be  noticed  that  one  of  the  enclosing  caps  has  a  circular 
extension  chamber  in  the  center;  this  is  for  the  accommodation  of  the 
commutator  and  brushes.  The  journals  are  self-oiling,  but  of  the  wick- 
feed  type  in  preference  to  the  usual  oil  ring  or  roller  form  of  feed.  The 
wick  feed  is  suggested  for  the  reason  that  the  pitching  or  rolling  of  the  boat 
is  likely  to  interfere  with  the  operation  of  an  oil  ring  by  jamming  it. 


i 


s       K 


FIG.  114 

The  commutator  is  not  shown,  it  being  considered  inadvisable  for  an 
amateur  to  attempt  the  construction  of  this  most  vulnerable  part  of  the 
machine.  A  finished  commutator  can  be  bought  from  any  one  of  the 
various  manufacturers  for  less  money  than  it  would  actually  cost  an 
amateur  to  build  one,  and  there  is  no  comparison  between  the  results. 
There  must  be  46  segments,  and  the  commutator  barrel  must  be  6  ins.  in 
diameter,  with  an  available  brush  tread  or  face  3^  ins.  wide,  measured 
parallel  with  the  shaft.  The  total  length  of  the  commutator  parallel  with 
the  shaft  must  not  exceed  5  ins.  The  connecting  lugs  must  be  of  such 
length  as  to  give  a  diameter  of  lof  ins.,  measured  from  tip  to  tip  of  dia- 
metrically opposite  lugs. 

The  machine  is  designed  for  the  use  of  two  sets  of  carbon  brushes, 


94  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

two  brushes  per  set;  each  brush  must  be  f  in.  thick  by  ij  ins.  wide,  so 
that  the  total  contact  surface  at  each  set  of  brushes  will  be  2\  sq.  ins. 
The  builder  can  use  his  own  judgment  as  to  the  type  of  brush-holder  to  be 
used,  but  should  remember  that  it  is  absolutely  necessary  to  have  a  reliable 
contact  of  low  resistance  between  each  brush  and  its  holder.  The  author 
recommends  the  well-known  Baylis  reaction  holder  and  brush.  The  two 
sets  of  brushes  should  be  mounted  precisely  60°  apart.  An  opening  is 
cored  in  the  upper  wall  of  the  commutator  chamber,  through  which  access 
to  the  brushes  may  be  had  without  removing  the  end  cap;  this  opening 


FIG.  115 

may  be  normally  closed  by  a  cover  conforming  to  the  circular  outline  of 
the  chamber. 

The  armature  winding  of  the  machine  is  of  the  two-path  type,  and 
comprises  46  coils  of  No.  u  double-cotton-covered  magnet  wire,  wound 
two  strands  in  parallel,  with  four  turns  per  coil.  The  two  strands  in 
parallel  should  be  wound  side  by  side,  so  that  a  cross-section  of  the  finished 
coil  will  show  two  wires  in  width  and  four  in  depth,  as  indicated  in  Fig.  1 16, 
which  shows  one  of  the  armature  slots  with  two  half  coils.  The  coils 
should  be  wound  around  two  f-in.  pegs,  located  9  3-16  ins.  apart,  as  indi- 
cated in  Fig.  117,  which  is  a  side  view  of  a  coil  wound  on  the  pegs,  ready 
to  be  formed.  The  illustration  shows  only  one  wire,  as  the  two  wires  are 
side  by  side.  The  convolutions  of  the  coils  should  be  secured  with  fine 


THREE  HORSE-POWER  LAUNCH  MOTOR 


95 


FIG.  116 


linen  thread  at  each  of  the  bends,  A  and  Z>,  and  also  at  the  two  points 
indicated  by  the  lines  B  and  C.  The  distance  from  A  to  B,  and  from  C  to 
D,  is  3  1-32  ins.,  the  distance  from  B  to  C  being  3!  ins.  Then  the  bends 
of  the  coil  should  be  clamped  from  the  points  A  and  D,  outward,  leaving 
the  two  stretches  of  wire  undamped  inside  of  the  centers  of 
the  bend.  Then  each  stretch  or  side  of  the  coil  should  be  held 
in  a  clamp,  with  long  jaws,  extending  from  B  to  C,  one  clamp 
being  applied  to  the  upper  stretch  and  one  to  the  lower  stretch 
of  wires,  and  the  two  sides  should  be  pulled  in  opposite  direc- 
tions until  a  plan  view  of  the  coil  resembles  Fig.  118.  Then 
it  should  be  carefully  covered  with  one  wrapping  of  German 
linen  tape,  each  layer  being  wound  with  a  half  lap,  so  that 
there  will  be  two  thicknesses  of  tape  over  the  wires.  Varnish 
the  tape  thoroughly  and  bake  the  coil  until  it  is  entirely  dry. 

The  coils  must  be  assembled  on  the  armature  core  so  that  there  will 

be  8  teeth  between  each 
side,  E  and  F,  Fig.  118. 
The  coils  must  be  put  on 
the  core  with  one  side  of 
each  coil  in  its  slot  and 
the  other  side  held  tempo- 
rarily above  the  core,  suc- 
cessive coils  being  slipped  under  those  already  in  slots  until  one  side  of 
every  coil  is  in  its  slot  and  each  coil  is  resting  on  the  armature  core  on 
the  other  side.  Then  the  other  sides  can  be  entered  in  the  proper  slots. 
When  the  coils  are  all  in  place  in  the  slots  they  should  be  secured  tempo- 
rarily by  two  retaining  bands  of 
twine  wrapped  around  the  core 
under  each  end.  Then  the  termi- 
nals should  be  carried  to  the  com- 
mutator, all  of  the  under  terminals 
being  put  in  first.  The  left-hand 
terminal  of  each  coil  should  be  car- 
ried to  the  left  and  the  right-hand 
terminal  to  the  right,  as  near  equal 
distances  as  possible,  the  two  ter- 
minals entering  commutator  seg- 
ments between  which  there  must 
be  14  other  commutator  segments;  this  is  true  of  every  armature  coil. 

After  the  ends  have  been  soldered  in,  a  binding  of  No.  19  tinned-iron 
wire  should  be  put  around  the  center  of  the  core,  being  wound  on  an  insu- 
lating strip  of  vulcanized  fiber  1-64  in.  thick;  another  binding  of  either 


FIG.  117 


FIG.  118 


96  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

strong  cord  or  thin  brass  wire  should  be  put  around  the  projecting  ends 
of  the  coils,  about  midway  between  the  end  of  the  armature  core  and  the 
extreme  end  of  the  coil  projections.  These  binding  wires  must  also  be 
wound  on  fiber  strips  1-64  in.  thick. 

The  field  winding  consists  of  No.  2  single-cotton-covered  magnet  wire, 
each  coil  containing  35  turns;  there  should  be  5  layers,  with  7  turns  in  each 
layer.  The  coil  should  be  wound  on  a  forming  block,  the  cross-section 
of  which  must  have  the  shape  and  dimensions  shown  by  Fig.  119.  After 
winding  the  coil  on  the  forming  block  it  should  be  tied  at 
all  four  corners  with  linen  thread,  in  order  to  hold  the  wires 
in  place  while  the  coil  is  being  removed  from  the  forming 
block  and  during  the  operation  of  taping.  After  remov- 
ing the  block  the  coil  must  be  insulated  with  two  wrap- 
pings of  German  linen  tape  wound  with  a  half  lap,  exactly 
like  the  armature  coils  were  covered,  the  exterior  being 
heavily  varnished  after  the  taping  is  completed.  After  varnishing,  the 
coil  should  be  baked  until  it  is  thoroughly  dry.  The  six  field  coils  are 
connected  up  in  series  in  the  usual  manner  to  give  alternate  north  and 
south  poles,  and  the  entire  field  winding  is  connected  in  series  with  the 
armature,  making  the  machine  a  simple  series- wound  motor;  speed  regu- 
lation being  obtained  by  changing  the  connections  of  the  batteries 
supplying  current  to  the  motor. 


CHAPTER  XII 
MULTIPOLAR  THIRTY-FIVE-LIGHT  INCANDESCENT  DYNAMO 

THE  present  machine  is  of  the  same  general  design  as  the  3-horse-power 
motor  described  in  Chapter  IX  of  this  book.  The  field  magnet  consists 
of  a  cast-iron  frame  into  which  are  set  wrought-iron  magnet  cores  having 
cast-iron  pole-pieces,  as  shown  in  the  semi-cross-section,  Fig.  120.  The 
cast-iron  ring  is  preferably  made  in  a  single  piece  and  the  wrought-iron 
cores  are  turned  to  a  very  slight  taper  and  drawn  into  holes  in  the  yoke 
ring  by  means  of  a  bolt  and  heavy  washer  from  the  outside.  Unless  the 
builder  has  excellent  machine-shop  facilities,  however,  and  is  an  expert 
machinist,  this  construction  will  be  found  rather  difficult,  as  it  is  necessary 
to  have  a  perfect  fit  between  the  taper  of  the  magnet  core  and  that  of  the 
hole  in  which  it  is  seated. 

As  an  alternative  the  magnet  frame  can  be  cast  in  two  pieces,  the 
division  being  along  the  line  X,  Fig.  122.  If  the  motor  is  built  in 
this  way,  each  half  must  be  chucked  and  the  joint  faced  off  fairly 
smooth,  although  it  is  not  necessary  to  have  a  perfect  joint,  as  no  mag- 
netic lines  of  force  pass  across  the  joint.  After  truing  up  the  abutting 
faces  of  each  half  of  the  magnet  ring,  the  two  halves  should  be  clamped 
together  with  1-32  in.  of  cardboard  in  between  them  and  four  straight 
holes  bored  for  the  reception  of  the  field-magnet  cores.  A  field-mag- 
net core  is  shown  by  Fig.  121.  The  cast-iron  pole-pieces  must  be 
accurately  fitted  to  the  ends  of  the  cores  and  pinned  permanently  in  place 
with  iron  pins. 

The  magnet  ring  and  pole-pieces  must  be  of  the  best  grade  of  pig 
iron  obtainable.  The  magnet  cores  should  be  made  of  Norway  wrought 
iron.  The  corners  of  the  pole-pieces  should  be  heavily  rounded  so 
that  no  sharp  edges  are  left.  The  length  of  the  pole-pieces  parallel  with 
the  shaft  is  the  same  as  its  width  at  right  angles  to  this  dimension.  The 
outside  diameter  of  the  magnet  ring  is  2of  ins.  The  extreme  breadth  of 
the  ring  parallel  with  the  shaft  is  8  ins.  The  other  dimensions  are  as 
follows : 

97 


98  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

INCHES 

Inner  diameter  of  yoke  ring • 17! 

A  —  Bore  of  armature  chamber 8 

B  —  Axial  length  of  pole  face 4 

C  —  Width  of  pole-piece,  tip  to  tip,  in  a  straight  line 4 

D  —  Radius  to  which  pedestal  seat  is  cut 8§ 

E  —  Thickness  of  yoke   ring i  f 

F  —  Distance  between  ribs 7 

G  —  Width  of  plane  surface  back  of  magnet  coil 6| 

H  —  Height,  base  line  to  armature  center 12 

O  —  Axial  length  of  pedestal  seat 4 

P  —  Straight-line  width  of  pedestal  (width  of  pedestal  seat  is  the 

same) 7 

Q  —  Length  of  pedestal  foot,  commutator  side 7 

The  dimensions  of  the  magnet  core  (Fig.  3)  are  as  follows: 

. At , 

y          m  p 

Diameter,  inches 3rV       3f\       3  re 

Length,  inches .    .2          3          i^ 

Fig.  122  is  an  edge  view  of  the  field-magnet  frame,  including  one  journal 
pedestal  shown  in  perspective,  and  the  other  in  cross-section.  After 
fitting  the  magnet  cores  into  place  in  the  ring,  the  pole-pieces  should  be 
bored  and  the  pedestal  seats  cut,  at  one  setting  of  the  frame.  Fig.  124  is 
a  cross-section  of  the  armature  core,  showing  the  details  of  construction. 
The  discs  are  mounted  on  a  cast-iron  drum,  which  is  provided  with  a 
flanged  head  and  a  hub,  7,  at  one  end,  the  other  end  being  open.  The 
discs  are  clamped  in  place  by  a  cast-iron  ring  which  is  provided  with  a 
hub,  /,  and  a  flange,  similar  to  those  at  the  other  end  of  the  drum.  The 
clamping  ring  is  drawn  to  place  by  means  of  eight  3-i6-in.  bolts  passing 
through  holes  in  the  clamping  ring  and  tapping  into  the  end  of  the  cast- 
iron  drum.  The  center  lines  of  two  of  these  bolts  are  indicated  at  s,  s. 
The  cast-iron  drum  must  have  a  key-seat  cut  in  it  so  that  the  discs  may  be 
positively  driven. 

Both  the  hub  on  the  end  of  the  drum  and  that  on  the  clamping  ring 
should  be  keyed  to  the  shaft,  so  that  there  will  be  no  liability  to  displace- 
ment. At  each  end  of  the  core  construction  a  disc  of  fiber  1-16  in.  thick 
should  be  provided,  as  indicated  by  the  heavy  black  lines  in  the  engraving. 
These  discs  must  be  toothed  exactly  like  the  core  discs,  so  that  the  ends 
of  the  magnetic  core  will  be  entirely  covered.  The  iron  core  discs  are 
yf  ins.  in  diameter,  with  a  central  hole  3  ins.  in  diameter,  and  36  slots 
9-32  in.  wide  by  i  1-16  ins.  deep;  the  slots  have  parallel  sides.  The  discs 
must  be  of  the  best  grade  of  charcoal  iron,  1-40  in.  thick.  The  dimensions 
of  the  armature-core  structure  are  as  follows: 


MULTIPOLAR  THIRTY-FIVE-LIGHT  INCANDESCENT  DYNAMO     99 


IOO 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


INCHES 

I  —  Length  of  hub  clear  through  (also  length  of  flanges) i; 

Bore  of  this  hub i 

J  —  Length  of  hub  clear  through i 

Bore  of  this  hub i 

K  —  Diameter  of  hubs 2; 

L  —  Internal  diameter  of  core  drum 2, 

M  —  Outer  diameter  of  core  drum 3 

N  —  Diameter  of  flange  and  clamping  ring 5/5- 

Thickness  of  flange  and  clamping  ring | 

The  two  journal  pedestals  are  exactly  alike  and  made  of  ordinary 
cast  iron.  The  base  must  be  turned  accurately  to  conform  to  the  circle 
to  which  the  pedestal  seat  of  the  magnet  frame  is  machined.  The  stand- 
ard, or  pedestal,  is  an  open  frame  of  J-in. 
metal;  the  box  is  of  the  ring-oiling  type,  with 
a  single  ring  hung  exactly  midway  of  the  jour- 
nal. Fig.  123  is  a  transverse  cross-section  of 
the  pedestal  and  box.  The  box  is  bushed;  the 
bushing  may  consist  of  a  brass  casting  turned 
to  shape,  or  it  may  be  made  by  babbitting  a  piece  of  thin  brass  tubing, 
the  outer  diameter  of  which  is  a  snug  fit  in  the  box.  The  oil  slot  across 
the  center  of  the  box  must  be  provided  with  a  suitable  covering  to  exclude 
dust.  Each  pedestal  should  be  bolted  to  the  magnet  frame  with  two 
f-in.  cap  screws.  The  pedestal  and  box  measurements  are  as  below: 


FIG.  121 


INCHES 

It 

2 

3 


P  —  Widest  part  of  standard 

R  —  Axial  length  of  oil  well   

S  —  Inner  length  of  oil  well   

T  —  Inner  width  of  oil  well 

t  —  Inner  radius  of  oil-well  bottom 

Q  —  Outside  diameter  of  box z\ 

V  —  Inside  diameter  of  box i  \ 

W  —  Outside  length  of  box 4 

Y  —  Length    of    bushing 3^ 

Bore  of  bushing i 

Z  —  Projection  of  box  beyond  oil-well  wall y£ 

Diameter  of  oil  ring 2\ 

Bore  of  oil  ring if 

Width  of  oil  ring | 

A  bearing  must  be  turned  on  the  outside  of  the  inner  end  of  the  pedestal 
on  the  commutator  side  of  the  machine,  as  indicated  in  Fig.  122,  to  accom- 
modate the  brush-holder  rigging,  which  may  be  copied  from  any  of  the 
standard  makes.  Four  carbon  brushes  are  required,  each  brush  \  in. 
thick  and  ij  ins.  wide;  the  four  must  touch  the  commutator  exactly  90° 
(18  segments)  apart,  center  to  center.  The  commutator  must  have  71 
segments,  and  may  measure  3  ins.  along  the  shaft,  extreme  length.  The 
commutator  core  must  be  bored  to  fit  the  portion,  c,  of  the  shaft,  and 
key-seated  to  correspond.  The  diameter  of  the  barrel  should  be  not  less 


MULTIPOLAR  THIRTY-FIVE-LIGHT  INCANDESCENT  DYNAMO       101 

than  3  ins.,  nor  more  than  4  ins.,  and  the  diameter  measured  at  the  con- 
necting lugs  must  not  exceed  7  ins.  The  brush  surface,  measured  parallel 
with  the  shaft,  must  be  2  ins.  long.  It  will  be  best  to  buy  the  commutator 
complete  from  one  of  the  several  makers  of  this  class  of  apparatus. 


FIG.  122 


Fig.  125  is  the  armature  shaft.     The  key-seats  are  all  f  in.  wide  and 
3-16   in  deep.     The  dimensions  of  the  shaft  are  as  follows: 


102 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


Diameter,  ins 
Length,    ins. 


Total 
j      Length 


The  field-magnet  coils  may  be  wound  directly  on  the  cores  or  on  bobbins 
made  of  thin  vulcanized  fiber.     If  they  are  wound  directly  on  the  cores, 

the  latter  must  be  wrapped  first  with  three 
layers  of  unbleached  cottons  and  painted  with 
insulating  varnish,  two  circular  coil  heads  of 
hard  fiber  being  first  fitted  to  the  large  part 
of  each  core.  The  coils  consist  of  No.  18 
single-cotton-covered  wire,  wound  to  a  depth 
of  if  ins.  exactly.  The  exact  number  of 
turns  is  immaterial,  except  that  all  four  coils 
must  contain  the  same  number  of  turns,  and 
as  many  turns  should  be  put  on  as  can  be  got 
in  the  space  available.  With  careful  winding 
the  builder  should  get  30  layers  in  each  coil, 
and  60  turns  per  layer,  making  1800  turns 
per  coil. 

Should  the  reader  prefer  to  wind  the  coils 
in  bobbins,  the  magnet  core  need  not  be 
wrapped,  of  course.  After  each  coil  is  com- 
pleted, secure  the  outer  end  and  cover  the 

outside  layer  with  unbleached  cottons  two  layers  deep,  heavily  varnished. 
Fig.  126  indicates  how  the  field  coils  should  be  connected  up. 
There    are    71     armature 


coils,  each  consisting  of  six 
turns  of  No.  13  double-cot- 
ton-covered magnet  wire.  The 
coils  are  wound  around  two 
^-in.  pegs  set  10}  ins.  apart, 
center  to  center,  all  of  the  turns 
being  wound  on  top  of  each 
other,  none  side  by  side.  Fig. 
127  shows  one  of  the  coils 
wound  on  the  two  pegs  and 
ready  for  shaping.  After  com- 
pleting the  winding  of  each 
coil  the  wire  should  be  tem- 


-I--H 


FIG.  124 


porarily  secured  by  means  of  linen  threads  tied  around  the  coil  at  each 
end  and  in  the  center  of  each  reach  of  the  coil.     When  all  the  coils  are 


MULTIPOLAR  THIRTY-FIVE-LIGHT  INCANDESCENT  DYNAMO    103 

wound  they  should  be  formed  in  pairs,  two  coils  being  placed  side  by  side 
with  strips  of  varnished  fuller  board  o.oi  in.  thick  between  them,  as  indi- 
cated by  Fig.  128,  and  bent  to  the  shape  shown  by  Fig.  129.  Before  bend- 
ing the  coils  to  shape,  the  ends  must  be  clamped  from  the  points  A  and  D 


FIG.  125 

outward  and  from  the  points  B  and  C  inward,  so  as  to  locate  the  bends 
accurately.  The  distance  from  A  to  B  and  from  C  to  D  is  3  ins.,  so  that 
the  distance  from  B  to  C  will  be  4^  ins. 

The  straight  reaches  of  the  coils  must  be  pulled  apart  far  enough  to 
enable  the  coil  to  go  into  two  slots 
on  the  armature  core  between  which 
there  are  eight  teeth.  Then  each 
pair  of  coils  should  be  carefully 
wrapped  with  one  layer  of  German 
linen  tape,  wound  with  a  half  lap, 
so  that  there  will  be  two  thicknesses 
of  the  tape  on  each  side  of  the  coils. 
Varnish  the  outer  surface  of  the  tape 
thoroughly,  then  bake  the  coils  at  a 
temperature  of  120  to  130  degrees 
until  they  are  thoroughly  dried.  If 
the  builder  prefer,  "linotape"  or 
any  other  oiled  tape  may  be  used, 
and  the  varnishing  thereby  elimi- 
nated. When  the  coils  are  assem- 
bled properly  on  the  core  there  will  be  two  coils  for  each  slot.  It  is  for 
this  reason  that  the  coils  are  made  up  in  pairs  as  described.  They  must 

be  assembled  on  the  core 
so  that  between  the  two 
sides  of  each  pair  of  coils 
there  will  be  eight  core 
teeth. 

When  the  coils  are  all 
in  place  they  should  be  se- 
cured temporarily  by  two  retaining  bands  of  twine  wrapped  around  the 
coils  at  each  end  just  outside  of  the  armature  core.  Then  the  terminals 
may  be  carried  to  the  commutator  lugs,  all  of  the  lower  terminals  being 
put  in  first.  The  terminals  should  be  carried  straight  out  to  the  com- 


FIG.  126 


FIG.  127 


104 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


mutator  and  care  must  be  taken  that  the  coils  are  connected  up  in  exactly 
the  same  fashion  all  the  way  around.  The  terminals  of  each  coil  are  con- 
nected to  two  neighboring  commutator  segments.  Having  put  all  the 
lower  terminals  in  place  in  proper  rotation,  the  builder  can  start  at  any 
convenient  point  with  the  upper  terminals,  being  sure  that  the  first  one 


FIG.  128 

goes  in  the  commutator  lug  immediately  alongside  of  the  lug  to  which  the 
other  terminal  of  that  coil  has  been  connected.  Having  started  properly, 
the  terminals  can  be  put  in,  one  after  the  other,  in  the  sequence  in  which 
they  project  from  the  armature  slots,  without  further  testing,  provided  the 
lower  terminals  have  all  been  put  in  in  proper  sequence. 

After  the  armature  terminals  have 
been  soldered  to  the  commutator 
lugs,  two  bindings  of  No.  18  tinned- 
iron  wire  should  be  put  on  around 
the  core,  one  binding  about  J  in. 
from  each  end  of  the  core;  each 
binding  should  be  about  i  in.  wide, 
measured  parallel  with  the  shaft. 
The  coil  projections  which  extend 
out  beyond  the  armature  core  proper 
must  be  bound  down  to  the  barrels 
which  support  them  by  means  of 
either  No.  20  brass  wire  wound  over  two  or  three  varnished  layers  of  can- 
vas or  else  heavy  linen  twine  wound  over  a  single  layer  of  canvas.  Only 
one  binder  will  be  necessary  at  each  end  of  the  armature  winding.  If 
there  is  an  appreciable  drop  in  the  wiring  between  the  dynamo  and  lamps, 
the  speed  should  be  increased  until  the  voltage  at  the  lamps  is  normal  at 
full  load,  with  all  the  rheostat  cut  out. 

The  principal  data  applying  to  the  machine  are  as  follows: 


FIG.  129 


E.m.f.  at  the  brushes  at  no  load 

Armature  speed 

Resistance  of  armature  winding,  warm 

Normal  armature  current 

Normal  current  delivered  to  external  circuit 
Normal  exciting  current  in  field  winding .  .  .  , 


115  volts 
1400  r.p.m. 
£  ohm 
19!  amp. 
1 8  amp. 
if  amp. 


The  lamp  rating  of  the  machine  (35  lamps)  is  based  on  the  use  of 
3j-watt  i6-candle-power  lamps.  With  3.i-watt  lamps  the  machine  will, 
of  course,  maintain  a  correspondingly  greater  number. 


CHAPTER  XIII 

A  SEVENTY-FIVE-LIGHT  INCANDESCENT  DYNAMO 

THE  dynamo  forming  the  subject  of  this  chapter  is  designed  to  maintain 
75  i6-candle-power  incandescent  lamps  at  1 10-120  volts.  The  field  magnet 
is  of  the  familiar  radial-pole  type  with  circular  yoke,  and  is  provided  with 
a  partial  " shrouding"  on  each  side  somewhat  similar  to  the  practice  ob- 
served by  the  Crocker- Wheeler  Company.  The  principal  object  of  this 
shrouding  is  to  give  the  machine  a  rather  more  finished  appearance  than 
it  would  have  without  it,  and  if  any  reader  who  may  undertake  to  build 
the  dynamo  prefers  to  leave  off  this  web  it  may  be  done  without  affecting 
the  operation  of  the  machine. 

Fig.  130  is  an  end  view  of  the  field- magnet  frame  minus  the  coils  and 
journal  boxes.  Fig.  131  is  a  plan  view  of  the  frame,  which  shows  the 
arrangement  of  the  projecting  feet  that  support  the  journal  pedestals,  and 
Fig.  132  is  a  sectional  view  on  a  line  through  the  center  of  the  field-magnet 
structure.  In  order  that  the  design  may  be  available  to  a  larger  number 
of  readers,  cast  iron  has  been  adopted  as  the  material  for  the  field  magnet 
instead  of  cast  steel,  which,  of  course,  is  the  usual  modern  practice.  The 
only  machine  work  necessary  on  the  field  magnet  is  boring  out  the  pole 
faces  and  tooling  the  seats  for  the  journal  pedestals,  all  of  which  must  be 
done  at  one  mounting  of  the  magnet  frame  in  order  to  insure  accurate 
alignment  between  the  armature  chamber  and  the  journals.  Fig.  133  is 
a  section  of  one  magnet  pole,  and  the  corresponding  part  of  the  yoke, 
taken  on  the  line  C-D  of  Fig.  130  and  Fig.  134,  is  a  cross-section  of  a 
magnet  core  taken  on  the  line  A-B  in  Fig.  132. 

The  dimensions  of  the  magnet  which  are  not  shown  in  the  drawings 
are  as  follows: 

INCHES 

Extreme  diameter  of  shell 17 

Extreme  diameter  over  the  ribs 18^ 

Distance  between  ribs 9 

Thickness  of  each  rib  parallel  with  shaft i 

Total  plan  length  of  field-magnet  frame  from  outside  to  outside  of 
journal  pedestal  seats 24^ 

I05 


io6  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

Figs.  135  and  136  are  sectional  views  of  a  journal  box  and  pedestal, 
the  former  being  an  axial  section  and  the  latter  a  transverse  section.  The 
section  of  Fig.  135  is  taken  on  the  line  J-K  of  Fig.  136,  and  the  section  of 
Fig.  136  is  taken  on  the  line  H-I  of  Fig.  135.  As  the  sketches  plainly 
show,  the  bearing  is  of  the  oil-ring  variety,  with  a  circular  reservoir,  and 
the  sleeve  is  perfectly  straight,  this  type  being  much  easier  for  an  amateur 
to  construct  than  a  self-aligning  bearing.  If  ordinary  care  is  taken  in 


FIG.  130 

cutting  the  seats  of  these  pedestals  and  in  turning  off  their  bases,  the 
bearings  cannot  fail  to  come  in  alignment  without  any  special  provision 
in  the  way  of  a  swiveling  bushing.  The  pedestals  and  journal  boxes  are 
of  cast  iron,  of  course,  and  the  bushing  may  be  made  either  of  solid  brass 
or  of  a  thin  seamless  brass  tube  babbitted.  On  the  inner  end  of  one  journal 
box  a  seat  \  in.  long  should  be  turned  for  the  brush-holder  yoke.  Only 
two  sets  of  brushes  are  required,  and  these  must  bear  upon  the  commutator 
exactly  one  fourth  of  a  circle  apart.  The  brush  yoke,  therefore,  may  be 
of  the  V  type  in  preference  to  the  ordinary  straight  arm  which  is  used  on 


A  SEVENTY-FIVE-LIGHT  INCANDESCENT  DYNAMO 


107 


bipolar  machines.  Returning  to  the  bearings,  the  oil  rings  will  be  2\  ins. 
in  diameter,  inside,  5-16  in.  wide  parallel  with  the  shaft,  and  \  in.  thick, 
measured  radially. 

Fig.  137  shows  the  shaft  and  a  sectional  view  of  the  armature  core  and 
supporting  drum.  This  drum  is  a  simple  cylinder,  d,  3  ins.  in  diameter 
outside  when  finished,  and  provided  with  a  flange,  g,  at  one  end,  which 
carries  at  its  outer  edge  a  drum  or  barrel,  b.  The  function  of  this  barrel 
is  to  support  the  projecting  ends  of  the  armature  coils.  The  discs  are 
mounted  on  the  drum,  d,  and  clamped  in  place  by  means  of  a  ring,  /•, 
which  carries  a  barrel,  b,  exactly  like  the  one  on  the  flange  of  the  core 
drum.  These  flanges  project  2j  ins.  from  the  core  discs.  The  ring,  r, 


FIG.  131 

may  be  secured  to  the  drum,  d,  by  means  of  six  3-i6-in.  machine  screws. 
The  dimensions  of  the  different  parts  of  the  shaft  are  marked  on  the  sketch, 
as  well  as  the  principal  dimensions  of  the  armature  core  and  spider;  those 
which  are  not  indicated  are  as  follows: 

INCHES 

Diameter  of  armature   discs 8 

Number    of    slots 4° 

Size  of  each  slot i  x  IT\ 

Diameter  of  extension  barrels 5t 

Diameter  of  core  hubs,  h 2 

Extreme  length  of  core  drum  from  end  to  end  of  the  hubs .  . 9^ 

Diameter  of  core  drums,  d 3 

Radial  thickness  of  drum  wall I 

Thickness  of  flange,  g,  and  ring,  r,  parallel  with  shaft i 


io8 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


The  commutator  should  be  purchased  from  some  of  the  standard 
manufacturers.  Its  extreme  length  along  the  shaft  must  not  be  over 
4\  ins.  It  must  have  79  segments,  and  should  be  not  less  than  5  ins.  in 
diameter.  The  width  of  the  brush  tread  parallel  with  the  shaft  must  be 
not  less  than  3  ins.,  and  the  diameter  from  tip  to  tip  of  diametrically  oppo- 
site connecting  lugs  must  be  7^  ins. 


FIG.  132 

The  machine  is  designed  for  the  use  of  carbon  brushes,  each  set  com- 
prising two  brushes  f  x  if  ins.  The  builder  can  exercise  his  own  judgment 
as  to  the  type  of  brush-holder  to  be  used,  but  should  remember  that  it  is 
indispensable  to  have  a  reliable  contact  of  low  resistance  between  the 
brush  and  the  holder.  As  noted  above,  there  are  only  two  sets  of  brushes, 
these  being  set  "on  the  quarter,"  or  90  degrees  apart. 

The  field  winding  of  the  machine  consists  of  four  coils  of  No.  18  double- 
cotton-covered  magnet  wire  wound  14  layers  deep  and  46  turns  long 
parallel  with  the  axis  of  the  core,  giving  644  turns  per  coil.  If  the  builder 
is  able  to  put  more  turns  than  this  without  exceeding  a  depth  of  11-16  in., 
so  much  the  better,  but  the  coil  should  not  be  deeper  than  this.  The  coils 


A  SEVENTY-FIVE-LIGHT  INCANDESCENT  DYNAMO 


log 


are  connected  up  in  the  usual  manner,  so  that  the  polarity  of  the  magnet 
cores  alternates,  and  a  rheostat  must  be  provided  to  regulate  the  field 
current.  As  in  the  case  of  the  commutator,  it  is  wholly  inadvisable  for 
an  amateur  to  attempt  the  construction  of  his  rheostat;  consequently,  no 
directions  are  given  for  this. 

Each  field  coil  must  be  taped  with  two  layers  of  German  linen  tape 


wound  through  the  coil  shuttle-fashion,  so  that  the  tape  crosses  the  wires 
at  right  angles.     As  in  the  case  of  the  armature  coils,  each  layer  of  taping 


L 


FIG.  135 


FIG.  136 


must  be  wound  with  a  half  lap,  varnished  and  thoroughly  dried,  i.e.,  the 
first  layer  must  be  thoroughly  dried  before  the  second  layer  of  tape  is  put 
on,  and  then  the  second  layer  must  be  varnished  and  dried  similarly. 
The  armature  winding  consists  of  79  coils  of  No.  8  double -cotton- 


no 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


covered  magnet  wire,  each  coil  containing  2  turns.  The  coils  must  be 
wound  in  pairs  around  two  f-in.  pegs,  as  indicated  in  Fig.  138,  the  four 
turns  (two  coils)  being  wound  one  on  top  of  the  other,  so  that  when  the 
pair  of  coils  is  finished  it  will  present  about  the  appearance  indicated  by 


'l  diam  Z\&  lone- 


FIG.  137 

the  sketch.  The  convolutions  of  the  coils  should  be  secured  with  fine 
linen  thread  at  the  points  indicated  by  the  lines  B  and  C,  and  also  at  the 
bends  A  and  D.  Then  the  bends  of  the  coils  should  be  clamped  from 

the  points  A  and  D  outward,  and 
the  two  straight  reaches  or  "sides" 
pulled  apart  until  the  plan  view 
of  the  coils  is  as  shown  in  Fig. 
139.  Then  the  wires  should  be 
wrapped  with  two  layers  of  Ger- 
man linen  tape,  with  half-lap,  so 
that  there  will  be  four  thicknesses 


FIG.  138 


of  tape  on  the  coils.  Each  layer  of  tape  should  be  thoroughly  varnished, 
and  the  completed  coil  baked  until  it  is  dry.  If  the  builder  prefers,  he 
may  use  "linotape"  instead  of  Ger- 
man linen,  and  omit  the  varnishing,  as 
" linotape"  is  thoroughly  impregnated 
with  oil. 

The  coils  must  be  put  in  the  core 
slots  so  that  each  pair  embraces  9 
teeth.  It  is  imperative  that  all  of  the 
coils  be  wound  exactly  alike  and  put  FlG  I39 

on  the  core  alike,  so  that  the  starting 

ends  of  all  of  them  will  occupy  the  same  relative  positions  when  all  are 
in  place  in  the  slots.  When  all  the  coils  are  in  the  slots,  they  should  be 
temporarily  secured  with  two  bands  of  binding  twine  around  the  core  at 


A  SEVENTY-FIVE-LIGHT  INCANDESCENT  DYNAMO  in 

each  end.  Then  the  coil  terminals  may  be  carried  to  the  commutator,  all 
of  the  under  terminals  being  put  in  the  lug  grooves  first  and  in  regular 
sequence. 

It  will  be  found  convenient  to  lead  the  under  coil  terminals  to  commu- 
tator segments  which  lie  about  20  bars  to  one  side  of  the  bar  opposite  the 
bend  of  the  coil,  and  the  upper  terminals  will  then  go  to  the  other  side  of 
the  bend  by  about  the  same  distance.  Having  put  all  of  the  under  terminals 
in  the  commutator  lugs,  start  at  any  convenient  place  to  put  the  upper 
terminals  in  place;  the  first  of  these  must  go  to  the  commutator  segment 
which  is  39  steps  from  the  one  to  which  the  under  terminal  of  the  same 
coil  is  connected.  In  other  words,  the  two  terminals  of  each  coil  must  be 
connected  to  two  commutator  bars  between  which  there  are  38  other  bars. 

After  the  coil  leads  have  been  soldered  to  the  commutator  lugs,  a 
binding  of  No.  18  tinned-iron  wire  should  be  put  around  the  center  of  the 
armature  core,  and  another  binding  of  No.  20  brass  wire  put  around  the 
projecting  parts  of  the  coils  at  each  end  of  the  core,  near  the  end  of 
the  supporting  barrel.  All  three  bindings  must  be  wound  on  fiber  strips 
not  less  than  1-32  in.  thick. 

The  rated  speed  of  this  machine  is  1500  r.p.m.,  at  which  speed  it  should 
give  115  to  120  volts  at  no  load,  with  no  resistance  in  the  field  circuit. 
If  it  fails  to  do  so,  it  will  be  on  account  of  the  quality  of  the  material  in 
the  field  magnet;  in  that  event  the  speed  must  be  increased  to  get  the  proper 
voltage.  The  armature  will  carry  44  amperes. 


CHAPTER  XIV 
FOUR-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 

THIS  machine,  so  far  as  the  field  magnet  and  all  mechanical  details 
are  concerned,  is  identical  with  the  75-light  dynamo  described  in  the  pre- 
ceding chapter.  The  only  differences  are  in  the  parts  and  features  de- 
scribed in  this  chapter. 

The  armature  core  has  32  slots,  each  5-16  x  i  1-16  ins. 

The  commutator  must  be  5  ins.  in  diameter  at  the  barrel  and  its  face 
2j  ins.  wide  parallel  with  the  shaft.  The  diameter  over  the  lugs  is  the 
same  as  in  the  75-Hght  dynamo.  It  must  have  32  segments. 

The  machine  is  designed  for  four  sets  of  copper  brushes,  opposite  sets 
being  connected  together,  of  course,  as  in  the  case.of  all  multipolar  machines. 
Each  set  comprises  two  brushes,  each  f  in.  thick  by  i  in.  wide;  the  ends 
of  the  brushes  must  be  beveled  to  such  an  angle  as  to  give  an  actual  con- 
tact surface  J  in.  by  i  in.  The  builder  can  use  his  own  judgment  as  to 
the  type  of  brush-holder,  although  there  is  not  much  latitude  when  it 
comes  to  designing  a  brush-holder  for  copper  brushes.  It  will  be  advisable 
to  copy  the  design  of  brush-holder  used  on  some  standard  machine. 

The  field  winding  of  the  machine  consists  of  four  coils  of  No.  1 1  single- 
cotton-covered  magnet  wire  wound  12  layers  deep  and  23  turns  long 
parallel  with  the  axis  of  the  core,  giving  276  turns  per  coil.  If  the  builder 
is  able  to  put  more  turns  than  this  without  exceeding  a  depth  of  13-16  in., 
so  much  the  better,  and  the  coil  should  not  be  deeper  than  this.  The 
coils  are  connected  up  in  the  usual  manner,  so  that  the  polarity  of  the 
field-magnet  cores  alternates,  and  a  rheostat  must  be  provided  to  regulate 
the  field  current.  As  in  the  case  of  the  commutator  it  is  inadvisable  for 
an  amateur  to  attempt  the  construction  of  a  rheostat,  and  for  this  reason 
no  instructions  are  given  for  this  work.  The  field  rheostat  must  be  able 
to  carry  50  amperes  continuously  without  overheating.  Each  field- magnet 
coil  must  be  taped  and  varnished  as  described  in  the  preceding  chapter. 

The  armature  winding  consists  of  32  coils  of  i  turn  each,  and  each 
consisting  of  two  No.  4  wires  in  parallel.  Fig.  140  shows  one  coil,  which, 

112 


FOUR-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 


A^ 


FIG.  140 


as  the  sketch  shows,  is  merely  a  loop  14  ins.  long  from  the  free  ends  to  the 
center  of  the  pin  around  which  the  loop  is  bent.  After  bending  the  loop 
to  shape  it  should  be  clamped  across  the  bend  at  the  line  D,  and  each  side 
clamped  individually  at  the  points  indicated  by  the  lines  C  and  5;  the 
bodies  of  the  clamps  here  must  be  within  the  space  between  the  two  lines, 
so  that  the  extreme  outer  edges 

of  the  clamp  coincide  with  the        — -—        B  c f 

lines  B  and  C.     Then  the  two 
sides  should  be  bent  apart  un- 
til a  plan  view  of  the  coil  looks 
like  Fig.   141.     After  it  is  in 
this  shape  it  should  be  care- 
fully taped  with  a  single  wrapping  of  German  linen  tape,  wound  with  a 
half  lap,  so  as  to  give  two  complete  thicknesses  of  the  tape.     After  tap- 
ing, each  coil  should  be  varnished  with  shellac  or  some  other  reliable 
armature  varnish  and  baked  until  it  is  thoroughly  dry. 

The  coils  must  be  assembled  on  the  armature  core  so  that  there  will  be 
7  teeth  between  the  two  sides  of  each  coil.  When  the  coils  are  all  in  posi- 
tion on  the  armature  core  they  should 
be  temporarily  secured  in  place  by 
two  retaining  bands  of  twine  wrapped 
around  the  coil  projections  at  each 
end  of  the  armature.  Then  the  coil 
connections  should  be  carried  to  the 
armature,  all  of  the  under  terminals 
being  pat  in  place  first  and  followed 
by  the  upper  terminals.  The  two 


FIG.  141 


terminals  of  each  coil  must  be  connected  to  neighboring  segments  of  the 
commutator.  Having  put  all  the  lower  terminals  in  the  commutator 
segments,  the  builder  can  start  at  any  convenient  place  with  the  upper 
ends,  and  after  the  upper  end  of  the  first  coil  is  put  in  the  segment  next 
to  the  lower  end  of  the  coil,  all  of  the  other  upper  ends  follow  in  regular 
rotation,  so  that  it  is  not  necessary  to  test  each  coil,  provided  the  under 
ends  have  all  been  inserted  in  proper  rotation  and  that  the  upper  terminal 
of  the  first  coil  is  properly  located. 


CHAPTER  XV 
A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 

THE  accompanying  engravings  are  reproductions  made  from  working 
drawings  for  the  construction  of  an  electroplater  having  a  capacity  of 
approximately  100  amperes  at  6  volts.  Figs.  142  and  145  are  assembly 
drawings  of  the  machine,  the  latter  being  a  complete  axial  section.  The 
yoke  ring  is  of  cast  iron,  and  it  is  intended  that  the  magnet  poles  shall  be 
made  of  round  wrought  iron  of  the  size  and  shape  indicated  by  Figs.  142 
and  143,  and  cast- welded  into  the  yoke  ring.  The  pole-face  curve  shown 
at  the  right-hand  end  of  the  magnet  core  in  Fig.  143  is  intended  to  be 
machined  before  the  poles  are  cast  into  the  yoke;  this  may  best  be  done 
by  mounting  the  cast-iron  pole-piece  (Fig.  144)  on  the  end  of  each  of  the 
poles,  clamping  the  four  poles  in  a  jig  and  boring  out  the  pole  faces.  Care 
must  be  taken  that  the  distance  from  the  left-hand  end  of  the  body  of  the 
magnet  pole  (Fig.  143)  to  the  center  of  the  pole  face  curve  is  exactly  3^  ins., 
as  marked  on  the  drawing,  and  when  the  poles  and  shoes  are  set  into  the 
mold,  prepatory  to  casting  the  yoke  ring,  ^  -tra  care  must  be  taken  to  see 
that  the  distance  between  diametrically  opposite  poles  is  6J  ins.,  as  specified 
in  Fig.  142.  It  will  be  found  a  good  plan  to  bolt  the  four  poles  to  a  central 
cast-iron  drum  so  as  to  secure  the  proper  alignment  when  they  are  set  into 
the  yoke-ring  mold. 

Two  journal-box  bracket  patterns  will  be  necessary,  since  the  bracket 
at  the  commutator  end  must  be  extended  farther  out  from  the  yoke  ring 
than  the  one  at  the  pulley  end  of  the  machine.  Fig.  146  is  a  face  view  of 
one  of  the  bracket  rings,  both  of  which  are  identical  from  this  view  point. 
The  journal-box  housings  are  shown  cast  in  a  single  piece  with  the  pedestal 
bracket  and  having  a  thick  web  straight  across  the  center  horizontally, 
which  is  bored  out  to  receive  the  bushing.  This  may  be  secured  in  place 
by  means  of  a  pin  set  into  one  side  of  the  housing  at  a  point  midway  be- 
tween the  oil-ring  slot  and  the  end  of  the  web  in  which  the  bushing  is  seated. 
This  arrangement  is  not  shown,  it  being  thought  best  to  leave  the  exact 
details  of  the  construction  to  the  individual  fancy  of  the  builder.  It  makes 

114 


A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO  115 

no  difference,  of  course,  what  the  details  of  the  box  construction  are  so 
long  as  the  bore  and  length  of  the  bushings  are  adhered  to  and  a  suitable 
projection  is  provided  on  the  inner  end  of  the  right-hand  housing  in  Fig.  145 
to  take  the  brush-holder  quadrant.  Fig.  147  shows  the  oil  ring,  which 


JL. 


FIG.  142 

should  be  made  of  a  rather  hard  grade  of  brass.     The  shaft  shown  in 
Fig.  149  may  be  made  of  ordinary  machine  steel. 

The  armature  is  of  the  usual  drum  construction,  and  the  discs  should 
be  cut  from  sheet  iron  not  more  than  25  mils  thick.     The  discs  must  be 


n6 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


6J  ins.  in  diameter  and  must  have  41  slots,  each  7-32  in.  wide  and  f  in. 
deep,  the  sides  of  the  slots  being  parallel  with  each  other.  The  corners 
at  the  bottoms  of  the  slots  should  be  rounded  to  1-16  in.  radius  in  order  to 


TT: 


-**iu. 


LL 


FIG.  143 

strengthen  the  teeth  and  also  to  increase  the  width  of  the  magnetic  path 
in  the  tooth  at  that  point.  The  discs  must  be  key-seated,  as  indicated  in 
Fig.  142,  the  key-seat  being  J  in.  deep  and  J  in.  wide.  The  key  is  to  be 
J  in.  square  and  without  any  taper,  of  course.  The  discs  are  clamped  on 
the  shaft  between  two  heads  of  the  size  and  construction  shown  in  Fig. 


FIG.  144 

149.  These  are  cast-iron  plates,  each  having  a  cylindrical  flange  extending 
axially  from  one  side  and  being  tapered  on  the  outer  face  so  as  to  form  a 
slanted  or  tapered  barrel  for  the  support  of  the  armature  coils  where  they 
extend  beyond  the  ends  of  the  core. 


A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 


117 


As  shown  clearly  in  Fig.  145,  the  clamping  head  at  the  end  of  the  arma- 
ture toward  the  pulley  backs  up  against  the  collar  on  the  shaft,  and  the  one 
at  the  end  toward  the  commutator  is  kept  in  place  by  the  round  nut  shown 
in  Fig.  148.  It  will  not  be  advisable  to  attempt  to  compress  the  discs  by 
screwing  up  this  nut;  the  proper  number  of  discs  (to  make  a  3~in.  core 
when  assembled  under  considerable  pressure)  should  be  slipped  on  the 
shaft  and  compressed  by  screw  pressure  applied  to  a  stout  plank  or  beam 
laid  across  the  end  of  the  armature  structure  and  having  a  3f-in.  hole 


Slot  for  oil  ring 


FIG.  145 

bored  in  it  into  which  the  barrel  of  the  clamping  end-plate  may  slip. 
After  the  discs  are  compressed  to  the  proper  position,  the  retaining  nut 
may  be  put  in  place  and  set  home  with  a  spanner  wrench  having  pins  at 
right  angles  to  the  handle  instead  of  pins  set  into  the  curved  face. 

The  commutator,  the  details  of  which  are  shown  in  Figs.  151  to  153, 
is  intended  to  be  4  ins.  in  diameter  at  the  barrel  and  6  ins.  over  the  lugs, 
but  the  diameter  of  the  barrel  may  be  reduced  to  3  ins.  if  preferred.  The 
core  (Fig.  152)  may  be  made  of  cast  iron,  but  is  preferably  made  of  hard 
cast  brass;  this  is  also  true  of  the  clamping  ring  shown  in  Fig.  153.  The 


n8 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


segments  must,  of  course,  be  made  of  copper,  either  drop-forged  or  cast; 
all  of  the  axial  and  radial  dimensions  are  shown  in  Fig.  151.  The  width 
of  each  segment  at  the  face,  measured  circumferentially,  as  well  as  the 
taper  of  the  segment  from  the  inner  edge  to  the  outer,  had  best  be  left  to 
the  manufacturer  from  whom  the  segments  are  obtained;  it  is  unwise  for 
an  amateur  to  attempt  the  actual  construction  of  his  segments.  Segments 
may  be  obtained  from  any  of  the  representative  makers  by  specifying  the 
number  of  segments,  the  diameter  of  the  commutator  barrel,  and  the  thick- 
ness of  insulation  between  the  segments,  which  should  be  30  mils. 


/ 

/ 

/ 

/ 

1 

/ 

1 

1 

1 

I 

1 

\ 

1 
\ 

\    \ 

\  \ 

\\ 

JfcBoss 


FIG.  146 

In  putting  the  commutator  together,  it  will  be  found  advisable  to  bore 
a  hole  4^  ins.  in  diameter  in  a  block  of  wood  ij  ins.  thick,  and  assemble 
the  segments,  together  with  the  mica  insulating  strips,  loosely  within  this 
hole.  Then  set  the  segments  up  tight  by  radial  pressure  from  the  outside, 
using  a  ring  of  either  cast  iron  or  wrought  iron  about  8J  ins.  in  diameter 
at  the  lug  end  of  the  commutator,  and  a  smaller  ring  of  6  ins.  inside  diameter 


A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 


IIQ 


f 


FlG   I47 


at  the  other  end;  these  rings  each  having  eight  J-in.  screws  extending 
through  them  radially  at  equal  intervals  around  the  circumference,  the 
screws  pressing  against  eight  segments  of  cast  iron,  which  in  turn  press  the 
commutator  segments  together.  The  point  of  each  screw  should  be  bedded 
in  a  shallow  hole  in  the  center  of  the  cast-iron  segment,  against  which  it 
presses  in  order  that  the 

segments    may    not    slip  — -H^K — 

out  from  under  the  screw. 
When  the  commuta- 
tor segments  have  been 

compressed  as  tightly  as      J  ff  \\      J 

possible,  so  as  to  form  as 
nearly  as  possible  a  true 
circle,  the  complete  struc- 
ture as  it  stands  should 
be  chucked  in  a  lathe 
and  the  ends  machined  to 
the  proper  tapers  to  fit  the  tapered  ring  on  the  commutator  core  (Fig. 
152)  and  the  clamping  ring  (Fig.  153).  The  core  should  then  be  inserted 

in  the  center  of  the  mass  of  seg- 
ments without  removing  the  ex- 
ternal clamps,  and  the  clamping 
ring  (Fig.  153)  put  in  place  and 
clamped  tightly  by  means  of  the 
nut.  The  external  assembling 
rings  and  block  may  then  be 
removed  and  the  commutator 
mounted  on  a  mandrel  and 
turned  true  on  the  outer  sur- 

FIG.  148  face- 

Fig.  156  shows  a  convenient 

form  of  slide  rail  which  may  be  used  with  the  machine  if  belt  adjustment 
is  desired.  The  feet  on  the  yoke  ring  of  the  machine  have  holes  drilled 


16  Threads  per  »n/-h 


FIG.  149 


in  them  to  match  the  slots  in  the  slide  rail,  as  indicated  in  Figs.  142  and 
145.     It  is  intended  simply  to  bolt  the  two  slide  rails  down  12  ins.  apart 


120 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


from  center  to  center  and  mount  the  machine  on  them,  using  screws  in  the 
lugs  of  the  slide  rails  for  adjusting  the  position  of  the  machine. 

The  armature  winding  is  of  the  straight-out  or  barrel  type  and  consists 


Frc.  150 

of  41  coils,  each  of  two  No.  8  wires  in  parallel.  The  coils  may  be  formed 
initially  by  taking  two  pieces  of  No.  8  wire  20  ins.  long  and  doubling 
them  together  in  the  center,  one  wire  passing  around  the  bend  on  the  out- 
side of  the  other,  as  indicated  in  Fig. 
154.  The  two  wires  should  be  tied 
temporarily  with  very  fine  linen  thread 
to  hold  them  in  place  during  the  form- 
ing. They  may  then  be  bent  to  the 
shape  shown  by  Fig.  155,  the  distance 
between  the  two  parallel  sides  of  the 
coil  being  made  such  that  the  coil  can 
be  put  into  two  armature  core  slots 
between  which  there  are  nine  teeth. 
After  being  bent  to  the  shape  shown, 
each  coil  should  be  given  a  single  wrapping  of  oiled  linen  tape  f  in.  wide 
and  o.oi  in.  thick,  wrapped  so  that  each  convolution  laps  over  one  half 
of  the  preceding  convolution. 

When  all  of  the  coils  have  been  made  ready,  the  slots  in  the  armature 
core  must  be  insulated  by  means  of  troughs  of  press  board  0.015  in.  thick, 


4.J 


Taper  )£  In  i 

FIG.  151 


A  ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO 


121 


and  the  barrel  at  each  end  must  be  given  two  layers  of  plain  linen  tape, 
heavily  varnished  after  being  wound  on.  The  pressboard  slot  troughs 
must  also  be  thoroughly  varnished  on  both  sides.  The  core  should  be 
put  in  an  oven  and  baked  until  the  varnish  on  the  troughs  and  the  taping 


16  Threads  per  inch 


FIG.  152 

is  thoroughly  dried  oat;  only  the  best  grade  of  orange  shellac  should  be 
used. 

The  coils  are  put  on  the  core  in  the  usual  manner,  all  of  the  under 
sides  being  put  in  the  slots  first  and  the  upper  halves  pulled  into  place  in 


Taper  j£in  l" 


FIG.  153 

proper  sequence  afterwards.  The  terminals  of  each  coil  must  be  connected 
to  commutator  segments  between  which  there  are  19  other  segments;  in 
the  usual  armature  winder's  parlance,  each  coil  will  be  connected  up  i  and 
21.  The  portions  of  the  winding  which  project  beyond  the  heads  of  the 
core  must  be  held  down  on  the  cast-iron  barrels  by  means  of  a  single  binding 
of  No.  1 8  brass  wire  at  each  end.  A  binding  of  No.  20  tinned-iron  wire 


122 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


should  be  put  on  the  center  of  the  core,  with  two  layers  of  pressboard 
between  the  wire  and  the  core.     The  bindings  on  the  coil  projections  at 


+-—*    Radius 


FIG.  154 

each  end  should  be  insulated  from  the  coils  by  means  of  three  or  four 

thicknesses  of  pressboard. 

The  field  winding  consists  of 
four  coils  of  No.  9  single-cotton- 
covered  wire,  wound  to  a  depth  of 
9  layers.  Each  coil  should  contain 
162  turns  of  wire,  so  that  the  length 
of  the  coil  parallel  with  the  core  will 
need  to  be  approximately  2\  ins. 
The  four  coils  are  to  be  connected 
in  series  and  the  entire  winding  is 
to  be  connected  in  shunt  to  the 
brushes,  with  a  suitable  rheostat  in 
series,  of  course.  The  shunt  field 
current  will  be  about  10  amperes 
and  the  rheostat  must,  of  course,  be 

proportioned  for  this  current.      The  coils  should  be  wound   on   bobbins 

of  either  brass  or  fiber,  the  barrel  of  the  bobbin  being  3  ins.  in  diameter 


FIG.  155 


KHj£t*H *X 

13!  " 


12  Threads 
chN 


4-1 


FIG.  156 

externally,  and  the  flanges  or  heads  5}  ins.  in  diameter.  If  brass  bobbins 
are  used,  these  must  be  thoroughly  insulated  with  varnished  muslin  or 
canvas  before  the  coils  are  wound  into  them.  The  exterior  of  each  coil 


A    ONE-HUNDRED-AMPERE  ELECTROPLATING  DYNAMO          123 

should  be  covered  with  a  layer  of  cord,  the  diameter  of  the  cord  being 
about  3-32  or  J  in. 

The  brushes  must  be  either  of  leaf  copper  or  woven  wire  and  each 
brush  face  must  be  f  x  if  ins.  Four  studs  and  brushes  must  be  used, 
one  brush  on  each  stud.  The  two  brushes  diametrically  opposite  will  be 
of  the  same  polarity,  of  course,  and  must,  therefore,  be  connected  by  means 
of  a  rubber-insulated  flexible  cable,  which  should  be  equal  in  conductivity 
to  No.  oooo  wire. 

The  principal  electrical  and  magnetic  data  relating  to  the  machine  are 
as  follows: 

Revolutions  per  minute 700 

E.m.f.  at  brushes 6  volts 

Delivered  armature  current 100  amperes 

Shunt  field  current 10  amperes 

Total  armature  current no  amperes 

Current  density  per  sq.  in.  in  armature  winding 2300  amperes 

Current  density  at  brush  faces no  amperes 

Current  density  in  field  winding 975  amperes 

On  account  of  the  difference  in  magnetic  quality  of  different  irons,  the 
speed  may  need  to  be  changed.  The  proper  speed  may  be  ascertained  by 
cutting  out  the  field  rheostat  and  driving  the  armature  at  whatever  speed 
is  necessary  to  give  7  volts  at  the  terminals;  this  should  be  taken  as  the 
running  speed  of  the  dynamo. 


CHAPTER  XVI 

SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR  OF  ONE-HALF 

HORSE-POWER 

THE  accompanying  drawings  give  all  of  the  essential  features  of  a 
self-starting  induction  motor  capable  of  giving  one-half  brake  horse-power 
on  a  single-phase  circuit  of  100  volts  and  125  to  133  cycles.  The  speed 
of  the  machine  will  depend,  of  course,  primarily  upon  the  frequency  of 
the  supply  current.  The  synchronous  speed  at  125  cycles  is  3750,  and  at 
133  cycles  it  is  4000  r.p.m.  The  actual  full-load  speed  will  be  something 
like  3300  r.p.m.  at  125  cycles  and  about  3500  r.p.m.  at  133  cycles. 

THE   STATOR 

Fig.  157  is  an  end  view  of  the  stator  and  Fig.  158  is  an  axial  section 
of  it,  showing  the  arrangement  of  the  brass  end  plates  and  the  bolts  that 
hold  the  structure  together.  The  stator  core  is  built  up  of  108  discs  of 
sheet  steel,  each  25  mils  thick,  and  allowing  for  scale  and  irregularities 
the  mass  should  be  drawn  together  tightly  enough  to  make  the  axial  thick-- 
ness 3  ins.,  as  indicated  in  the  engraving.  The  stator  discs  are  7  ins.  in 
diameter  outside,  and  the  hole  in  the  center  is  3  17-32  ins.  in  diameter; 
this  latter  measurement  must  be  absolutely  exact.  The  24  slots  around 
the  edge  of  the  central  hole  are  to  be  punched  by  means  of  the  simple 
punch  and  die  shown  by  Figs.  159  and  160,  these  being  used  in  a  step-by- 
step  notching  press.  It  is  not  assumed  that  the  builder  will  possess  one 
of  these  presses  or  buy  one  for  the  purpose  of  building  this  one  motor; 
but  he  can  easily  make  the  punch  and  die  and  have  the  work  done  at 
some  shop  where  such  presses  are  in  use. 

PUNCH  AND   DIE 

The  punch  is  built  up  in  three  pieces,  a  shank  and  holder  plate  of 
cast  iron,  a  punch  pad  of  ordinary  machine  steel,  and  the  punch  proper, 
of  annealed  steel.  The  punch  pad  is  a  simple  rectangular  plate,  in  the 
center  of  which  is  worked  a  socket  for  the  punch,  the  outline  of  this  socket 


SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR  125 

being  the  same  as  that  of  the  main  portion  of  the  opening  in  the  die.  The 
punch  is,  of  course,  of  the  same  outline  on  its  face  as  the  complete  opening 
in  the  die,  and  the  upper  part  of  it  is  to  be  made  a  very  snug  fit  in  the  hole 
in  the  punch  pad.  The  latter  is  secured  to  the  punch  holder  by  means 
of  four  J-in.  flat-head  machine  screws.  In  machining  the  holder,  great 
care  must  be  taken  to  have  the  face  of  it  absolutely  at  right  angles  with 
the  axis  of  the  shank.  The  wall  of  the  socket  in  the  punch  pad  must  also 
be  precisely  at  right  angles  with  the  face  that  matches  the  face  of  the  holder 
plate. 


FIG.  157 

Fig.  159  shows  the  punch  pad  partly  unscrewed  from  the  holder,  and 
the  punch  removed  from  its  socket;  it  is  held  in  the  socket  by  means  of  a 
J-in.  round-nosed  set-screw,  and  a  depression  should  be  machined  in  the 
side  of  the  punch  to  allow  the  nose  of  the  set-screw  to  seat  itself  without 
having  to  burr  the  punch.  After  the  punch  has  been  filed  to  shape,  it 
must  be  tempered.  In  first  hardening  it,  the  steel  should  be  heated  to  a 
bright  red  and  "quenched"  in  oil  or  lukewarm  water;  if  very  cold  water 
is  used  the  steel  will  be  too  brittle.  The  temper  should  be  drawn  in  the 
flame  of  a  Bunsen  burner,  and  the  steel  should  be  wiped  frequently  with 
an  oily  rag  during  the  heating.  If  the  reader  is  not  familiar  with  the 


126 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


process  of  "drawing"  the  temper  of  tool  steel,  he  had  better  get  this  done 
by  an  experienced  workman. 

The  die  is  to  be  made  of  annealed  steel,  of  the  quality  used  for  this 
class  of  work  (any  dealer  will  supply  the  proper  quality  if  told  what  it  is 
to  be  used  for).  The  sketches  show  clearly  the  shape  and  dimensions  of 
the  die.  The  dotted  line  arcs  in  the  upper  part  of  the  drawing  indicate 
the  inner  and  outer  edges  of  the  stator  disc  when  in  position  for  punching. 
The  hole  in  the  die  may  be  most  readily  cut  by  first  drilling  two  holes 
f  in.  in  diameter  and  one  hole  J  in.  in  diameter  along  a  straight  line  scribed 


FIG.  158 

on  the  face  of  the  die  block;  the  distances  from  center  to  center  of  these 
holes  are  stated  in  the  supplementary  sketch  between  the  plan  view  and 
the  side  view  of  the  die.  Having  drilled  these  three  holes,  the  superfluous 
metal  must  be  filed  away  slowly  and  very  carefully  until  the  desired  shape 
of  slot  is  obtained.  Then  the  hole  must  be  enlarged  on  the  under  side 
of  the  die  block  in  order  to  give  clearance  for  the  small  pieces  punched 
out  of  the  stator  discs  to  free  themselves. 

The  die  is  bolted  to  the  bolster  (which  need  not  be  made  by  the  ama- 
teur, as  the  shop  in  which  the  punching  is  done  will  have  bolsters  from 


SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR 


127 


which  an  appropriate  selection  may  be  made)  by  means  of  two  cap  screws 
and  two  flat-head  machine  screws.  The  cap  screws  also  hold  the  stripper 
plate,  which  is  a  rectangular  steel  plate  J  in.  thick  and  of  the  same  outline 
as  the  base  of  the  die  block ;  it  must  have  a  hole  cut  in  it  which  will  come 
directly  over  the  hole  in  the  die,  but  the  hole  in  the  stripper  need  not  be 
accurately  machined  to  the  shape  of  the  punch ;  it  may  be  a  simple  rect- 
angular  aperture  f  in.  wide  and  i  in.  long.  After  the  hole  in  the  die  has 
been  finished  to  fit  snugly  about  the  punch,  which  must  touch  every  part 


i 


Punch  Holder 


[lfe'<  -  ^-i/Screws  - 


& 


Preliminary  holes 
/  Stripper 


i   Die 


FIG.  159 


FIG.  i 60 


of  the  wall  of  the  die  hole,  the  die  is  to  be  tempered.     The  remarks  con- 
cerning the  tempering  of  the  punch  apply  also  to  the  die. 


CLAMPING   PLATES   AND   ASSEMBLY 

The  brass  end  plates  are  cast  with  the  slots  in  them,  the  sizes  of  the 
slots  in  these  plates  being  a  trifle  full,  as  compared  with  the  punched  slots 
in  the  core  discs.  It  will  not  do  to  use  a  simple  brass  ring  of  an  internal 
diameter  large  enough  to  clear  the  slots  in  the  core;  the  teeth  between 
these  slots  must  be  clamped  together  tightly  along  with  the  body  portion 
in  order  to  reduce  as  far  as  possible  the  humming  of  the  machine  when  in 
operation.  In  assembling  the  core  discs  between  the  brass  end  plates, 
the  structure  must  be  clamped  together  by  means  of  two  heavy  cast-iron 


128 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


discs  5  ins.  in  diameter  and  a  i-in.  bolt  through  the  center;  this  work 
may  be  facilitated  greatly  by  the  use  of  ordinary  iron  clamps  such  as  are 
found  in  all  machine  shops,  applying  these  at  points  around  the  outer 
edge  of  the  stator  in  order  to  even  up  the  compression  and  assist  the 
central  clamping  bolt.  After  the  discs  are  drawn  to  position,  the  holes 
near  the  outer  edge  may  be  drilled;  if  the  brass  end  plates  have  been 
made  of  a  hard  alloy,  the  top  one  will  serve  as  a  jig  for  the  drill.  In 
this  event  it  should  be  drilled  before  assembling  the  core  discs,  but  the 
under  plate  should  be  left  undrilled;  when  the  discs  are  assembled,  the 
holes  may  be  drilled  clear  through  them  and  the  under  brass  plate.  A 
much  safer  plan,  however,  is  to  make  a  cast-iron  jig  plate  and  clamp  the 
discs  between  it  and  a  plain  cast-iron  plate  for  drilling;  the  brass  end 
plates  should  be  drilled  by  the  same  jig  plate,  but  separately. 


FIG.  161 


The  four  f-in.  bolts  which  hold  the  stator  core  together  also  serve  to 
hold  the  journal  brackets  or  end  caps  in  place.  Fig.  161  shows  a  face 
view  of  one  of  these  end  caps  and  an  axial  section  through  the  center  of 
it.  The  drawings  require  no  explanation  beyond  saying  that  the  caps 
are  to  be  made  of  cast  iron.  (Figs.  157  and  158  show  the  stator  turned 
45  degrees  from  the  position  that  it  occupies  when  clamped  between  the 
journal  brackets,  or  end  caps,  this  being  done  to  show  the  bolts  in  the 
sectional  view.) 

The  journal  sleeves  shown  in  the  engraving  are  of  the  self-aligning  type, 
but  if  the  reader  is  not  verv  skilful  at  machine  tool  work  .it  will  be  pref- 


SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR 


129 


erable  to  make  them  perfectly  straight,  making  the  outer  diameter  of  the 
sleeves  f  in.  the  whole  length.  No  pulley  has  been  shown,  as  this  can  be 
bought  for  less  than  it  would  cost  an  amateur  to  make  it.  The  proper 
size  is  2\  or  2|  ins.  diameter  at  the  crown  and  ij  ins.  width  of  face. 


FIG.  162 


THE   ROTOR 

The  rotor  is  shown  by  Fig.  162.  It  consists  of  108  discs  of  sheet  steel 
clamped  on  the  shaft  between  two  cast-brass  end  plates,  which  also  serve 
to  connect  the  ends  of  the  rotor  conductors.  There  are  17  of  these,  each 
|  in.  in  diameter  and  4  ins.  long;  the  holes  in  the  rotor  discs  are  13-32  in. 
in  diameter,  and  may  be  drilled  with  the  aid  of  two  cast-iron  plates  between 
which  the  discs  are  temporarily  clamped,  one  of  the  cast-iron  plates  to  be 
previously  drilled  so  as  to  serve  as  a  jig  for  the  drill  when  the  discs  are 
drilled. 

WINDINGS 

After  the  stator  is  finished  the  slots  and  end  surfaces  of  the  core  should 
be  insulated  by  means  of  red  rope  paper  0.015 
in.  (15  mils)  thick,  which  should  be  thoroughly 
varnished  with  shellac  before  being  put  in 
place.  The  main  stator  winding  consists  of 
four  sections  or  coils  of  56  turns  each,  of  No.  14 
double- cotton- covered  magnet  wire,  but  this 
should  not  be  put  on  until  the  starting  winding 
is  in  place.  This  winding  consists  of  four  coils 
of  No.  14  wire,  each  having  28  turns.  Each 
of  these  coils  should  be  wound  into  the  proper 
slots  over  two  blocks  of  wood  (one  at  each  end 
of  the  core,  as  indicated  in  Fig.  163)  which 
will  cause  the  coils  to  project  f  in.  beyond  the 
face  of  the  stator  end  plates.  After  they  are  FlG-  l63 

wound  in  place  these  projecting  ends  are  to  be  bent  upward  out  of  the 
way  of  the  main  coils,  which  must  be  wound  in  the  slots  between  those  of 


130 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


the  starting  winding.  Fig.  164  indicates  this  bending  upward  of  the  start- 
ing coils  and  also  shows  the  slots  into  which  they  are  to  be  wound.  They 
are  connected  in  series  with  each  other,  and  the  connections  must  be  such 
that  if  direct  current  were  passed  through  this  winding  it  would  produce 
alternate  north  and  south  poles  within  the  four  coils. 

After  the  starting  winding  is  in  place  and  connected  up,  the  main  coils 
should  be  wound  into  their  slots;  two  thicknesses  of  varnished  muslin 
must  be  laid  over  the  exposed  parts  of  the  starting  winding  just  before 
commencing  the  winding  in  of  the  main  coils.  These  coils  are  to  be  wound 
in  their  slots  as  indicated  by  the  elementary  diagram,  Fig.  164;  this  shows 


FIG.  164 

only  one  turn  in  each  slot,  but  the  reader  will  of  course  understand  that 
26  turns  are  to  be  wound  in  the  inner  pair  of  slots  7,  7,  before  any  wire 
is  wound  in  the  outer  pair,  77,  77.  The  coils  of  the  main  winding,  like 
those  of  the  starting  winding,  must  be  connected  up  in  series  and  in  such 
wise  that  direct  current  passing  through  them  would  produce  four  magnetic 
poles  of  alternate  polarity:  north,  south,  north,  south.  It  makes  no  differ- 
ence what  the  relation  is  between  the  direction  of  the  starting  coils  and 
that  of  the  main  coils;  the  terminals  must  be  carried  out  to  a  three-pole, 


SELF-STARTING  SINGLE-PHASE  INDUCTION  MOTOR 


To  Line 


e     =     = 


double-throw  knife-blade  switch,  as  indicated  in  Fig.  165,  and  if  the  con- 
nections at  first  made  do  not  start  the  motor  in  the  direction  in  which  it  is 
intended  or  desired  to  run,  it  may  be  reversed  by  merely  reversing  the  leads 
from  either  the  main  winding  or  the  starting  winding,  but  not  both.  The 
switch  should  be  mounted  so  that  the  throw  is  horizontal  (unless  an  addi- 
tional main  switch  is  provided),  in 
order  that  it  may  be  left  open  with- 
out danger  of  accidentally  closing 
by  gravity.  As  the  diagram  is 
drawn,  throwing  the  switch  to  the 
left  puts  in  both  windings,  for 
starting  up;  when  the  machine 
attains  something  like  normal 
speed,  the  switch  should  be  thrown 
quickly  to  the  other  side,  leaving 
only  the  main  winding  in  circuit. 
If  the  builder  prefers  to  use 
simpler  apparatus,  two  ordinary 
double-pole  switches  may  be  used, 
one  for  the  main  winding  and  one 
for  the  starting  winding,  but  this 
arrangement  has  the  slight  disad- 
vantage that  the  user  may  close 


~2=    - 

e     ±     d 

•• 

JT  ,    1 
T    -     e   -    ] 

f 

one  switch  and  leave  it  closed  for 

an  appreciable  length  of  time  be- 

fore closing  the  other,  which  might 

overheat  the  winding  thus  thrown 

in  alone,  as  the  motor  would  not 

start  up  and  the  winding  would 

be  provided  with  a  short-circuited 

secondary  —  the  rotor  conductors.     The  result  would  be  similar  in  kind, 

though  less  in  degree,  to  that  obtained  by  short-circuiting  the  secondary 

terminals  of  an  ordinary  transformer  with  the  primary  connected  to  the 

supply  mains.     The  motor  should  not  be  started  with  any  load  on  it  ex- 

cept the  countershaft  to  which  it  is  belted.     Even  with  that  it  will  be 

found  advisable  to  give  the  belt  a  strong  pull,  to  overcome  standing  friction, 

when  the  motor  is  thrown  into  circuit. 


CHAPTER  XVII 

ONE-HORSE-POWER  SELF-STARTING  SINGLE-PHASE  INDUCTION 

MOTOR 

THE  machine  herein  described  is  similar  to  the  one  described  in  the 
previous  chapter.  It  is  a  self-starting  induction  motor  capable  of  giving 
one  brake  horse-power  on  a  single-phase  circuit  of  100  volts  and  125  to 
133  cycles.  The  speed  of  the  machine  will  depend,  of  course,  primarily 
upon  the  frequency  of  the  supply  current.  The  synchronous  speed  at 
125  cycles  is  3750,  and  at  133  cycles  it  is  4000  r.p.m.  The  actual  full-load 
speed  will  be  something  like  3300  r.p.m.  at  125  cycles  and  about  3500  r.p.m. 
at  133  cycles. 

THE    STATOR 

Fig.  1 66  is  an  end  view  of  the  stator  and  Fig.  167  is  an  axial  section 
of  it,  showing  the  arrangement  of  the  brass  end  plates  and  the  bolts  that 
hold  the  structure  together.  The  stator  core  is  built  up  of  225  discs  of 
sheet  steel,  each  20  mils  thick,  and  allowing  for  scale  and  irregularities 
the  mass  should  be  drawn  together  tightly  enough  to  make  the  axial 
thickness  5  ins.,  as  indicated  in  the  engraving.  The  stator  discs  are 
7f  ins.  in  diameter  outside,  and  the  hole  in  the  center  is  4  3-32  ins.  in 
diameter;  this  latter  measurement  must  be  absolutely  exact.  The  24  slots 
around  the  edge  of  the  central  hole  are  to  be  punched  by  means  of  the 
simple  punch  and  die  shown  by  Fig.  168,  these  being  used  in  a  step-by-step 
notching  press.  It  is  not  assumed  that  the  builder  will  possess  one  of 
these  presses  or  buy  one  for  the  purpose  of  building  this  one  motor;  but 
he  can  easily  make  the  punch  and  die  and  have  the  work  done  at  some  shop 
where  such  presses  are  in  use. 

THE    PUNCH 

The  punch  is  built  up  in  three  pieces,  a  shank  and  holder  plate  of 
cast  iron,  a  punch  pad  of  ordinary  machine  steel,  and  the  punch  proper, 
of  annealed  steel.  The  punch  pad 'is  a  simple  rectangular  plate  in  the 
center  of  which  is  worked  a  socket  for  the  punch,  the  outline  of  this  socket 

132 


ONE-HORSE-POWER  SELF-STARTING  INDUCTION  MO7OR         133 


134  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

being  the  same  as  that  of  the  main  portion  of  the  opening  in  the  die.  The 
punch  is,  of  course,  of  the  same  outline  on  its  face  as  the  complete  opening 
in  the  die,  and  the  upper  part  of  it  is  to  be  made  a  very  snug  fit  in  the  hole 
in  the  punch  pad.  The  latter  is  secured  to  the  punch  holder  by  means 
of  four  J-in.  flat-head  machine  screws.  In  machining  the  holder,  great 
care  must  be  taken  to  have  the  face  of  it  absolutely  at  right  angles  with 
the  axis  of  the  shank.  The  wall  of  the  socket  in  the  punch  pad  must  also 
be  precisely  at  right  angles  with  the  face  that  matches  the  face  of  the  holder 
plate. 

Fig.  1 68  shows  the  punch  pad  partly  unscrewed  from  the  holder,  and 


O 


1 


\ 


\ 


\*-/1r: 
Prelirnina'r}'  holes 

» 

FIG.  i 68 


the  punch  removed  from  its  socket;  it  is  held  in  the  socket  by  means  of  a 
J-in.  round-nosed  set-screw,  and  a  depression  should  be  machined  in  the 
side  of  the  punch  to  allow  the  nose  of  the  set-screw  to  seat  itself  without 
having  to  burr  the  punch.  After  the  punch  has  been  filed  to  shape,  it 
must  be  tempered.  In  first  hardening  it,  the  steel  should  be  heated  to  a 
bright  red  and  " quenched"  in  oil  or  lukewarm  water;  if  very  cold  water 
is  used  the  steel  will  be  too  brittle.  The  temper  should  be  drawn  in  the 
flame  of  a  Bunsen  burner,  and  the  steel  should  be  wiped  frequently  with 
an  oily  rag  during  the  heating.  If  the  reader  is  not  familiar  with  the 
process  of  " drawing"  the  temper  of  tool  steel  he  had  better  get  this  done 
by  an  experienced  workman. 

THE  DIE 

The  die  is  to  be  made  of  annealed  steel,  of  the  quality  used  for  this 
class  of  work  (any  dealer  will  supply  the  proper  quality  if  told  what  it  is 


ONE-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR         135 

to  be  used  for).  The  sketches  show  clearly  the  shape  and  dimensions  of 
the  die.  The  dotted-line  arcs  indicate  the  inner  and  outer  edges  of  the 
stator  disc  when  in  position  for  punching.  The  hole  in  the  die  may  be 
most  readily  cut  by  first  drilling  two  holes  f  in.  in  diameter  and  one  hole 
J  in.  in  diameter  along  a  straight  line  scribed  on  the  face  of  the  die  block; 
the  distances  from  center  to  center  of  these  holes  are  stated  in  the  supple- 
mentary sketch  between  the  plan  view  and  the  side  view  of  the  die.  Having 
drilled  these  three  holes,  the  superfluous  metal  must  be  filed  away  slowly 
and  very  carefully  until  the  desired  shape  of  slot  is  obtained.  Then  the 
hole  must  be  enlarged  on  the  under  side  of  the  die  block  in  order  to  give 
clearance  for  the  small  pieces  punched  out  of  the  stator  discs  to  free 
themselves. 

The  die  is  bolted  to  the  bolster  (which  need  not  be  made  by  the  ama- 
teur, as  the  shop  in  which  the  punching  is  done  will  have  bolsters  from 
which  an  appropriate  selection  may  be  made)  by  means  of  two  cap  screws 
and  two  flat-head  machine  screws.  The  cap  screws  also  hold  the  stripper 
plate,  which  is  a  rectangular  steel  plate  J  in.  thick  and  of  the  same  outline 
as  the  base  of  the  die  block;  it  must  have  a  hole  cut  in  it  which  will  come 
directly  over  the  hole  in  the  die,  but  the  hole  in  the  stripper  need  not  be 
accurately  machined  to  the  shape  of  the  punch ;  it  may  be  a  simple  rectan- 
gular aperture  f  in.  wide  and  i  in.  long.  After  the  hole  in  the  die  has  been 
finished  to  fit  snugly  about  the  punch,  which  must  touch  every  part  of  the 
wall  of  the  die  hole,  the  die  is  to  be  tempered.  The  remarks  concerning 
the  tempering  of  the  punch  apply  also  to  the  die. 

STATOR   CLAMPING   PLATES   AND   ASSEMBLY 

The  brass  end  plates  are  cast  with  the  slots  in  them,  the  sizes  of  the 
slots  in  these  plates  being  a  trifle  full,  as  compared  with  the  punched  slots 
in  the  core  discs.  It  will  not  do  to  use  a  simple  brass  ring  of  an  internal 
diameter  large  enough  to  clear  the  slots  in  the  core;  the  teeth  between 
these  slots  must  be  clamped  together  tightly  along  with  the  body  portion 
in  order  to  reduce  as  far  as  possible  the  humming  of  the  machine  when  in 
operation.  In  assembling  the  core  discs  between  the  brass  end  plates, 
the  structure  must  be  clamped  together  by  means  of  two  heavy  cast-iron 
discs  5!  ins.  in  diameter  and  a  i-in.  bolt  through  the  center;  this  work 
may  be  facilitated  greatly  by  the  use  of  ordinary  iron  clamps  such  as  are 
found  in  all  machine  shops,  applying  these  at  points  around  the  outer 
edge  of  the  stator  in  order  to  even  up  the  compression  and  assist  the  central 
clamping  bolt.  After  the  discs  are  drawn  to  position,  the  holes  near  the 
outer  edge  may  be  drilled;  if  the  brass  end  plates  have  been  made  of  a 
hard  alloy,  the  top  one  will  serve  as  a  jig  for  the  drill.  In  this  event  it 


136  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

should  be  drilled  before  assembling  the  core  discs,  but  the  under  plate 
should  be  left  undrilled;  when  the  discs  are  assembled,  the  holes  may  be 
drilled  clear  through  them  and  the  under  brass  plate.  A  much  safer 
plan,  however,  is  to  make  a  cast-iron  jig  plate  and  clamp  the  discs  between 
it  and  a  plain  cast-iron  plate  for  drilling;  the  brass  end  plates  should  be 
drilled  by  the  same  jig  plate,  but  separately. 

JOURNAL  BRACKETS 

The  four  f-in.  bolts  which  hold  the  stator  core  together  also  serve  to 
hold  the  journal  brackets  or  end  caps  in  place.  Fig.  169  shows  one  of 
these  end  caps  and  an  axial  section  through  the  center  of  it.  The  drawings 
require  no  explanation  beyond  saying  that  the  caps  are  to  be  made 
of  cast  iron.  (Figs.  166  and  167  show  the  stator  turned  45  degrees 
from  the  position  that  it  occupies  when  clamped  between  the  journal 
brackets,  or  end  caps,  this  being  done  to  show  the  bolts  in  the  sectional 
view.) 

The  journal  sleeves  shown  in  the  engraving  are  of  the  self-aligning 
type,  but  if  the  reader  is  not  very  skilful  at  machine  tool  work  it  will  be 
preferable  to  make  them  perfectly  straight,  making  the  outer  diameter  of 
the  sleeves  }  in.  the  whole  length.  No  pulley  has  been  shown,  as  this  can 
be  bought  for  less  than  it  would  cost  an  amateur  to  make  it.  The 
proper  size  is  3  or  3^  ins.  in  diameter  at  the  crown  and  i  J  ins.  width  of 
face. 

THE   ROTOR 

The  rotor  is  shown  by  Fig.  170.  It  consists  of  225  discs  of  sheet  steel 
20  mils  thick,  clamped  on  the  shaft  between  two  cast-brass  end  plates, 
which  also  serve  to  connect  the  ends  of  the  rotor  conductors.  There  are 

17  of  these,  each  9-16  in.  in  diameter  and  6  ins.  long;  the  holes  in  the  rotor 
discs  are  19-32  in.  in  diameter,  and  may  be  drilled  with  the  aid  of  two 
cast-iron  plates  between  which  the  discs  are  temporarily  clamped,  one  of 
the  cast-iron  plates  to  be  previously  drilled  so  as  to  serve  as  a  jig  for  the 
drill  when  the  discs  are  drilled. 

STATOR   WINDINGS 

After  the  stator  is  finished  the  slots  and  end  surfaces  of  the  core  should 
be  insulated  by  means  of  red  rope  paper  0.025  in.  (25  mils)  thick,  which 
should  be  thoroughly  varnished  with  shellac  before  being  put  in  place. 
The  main  stator  winding  must  not  be  put  on  until  the  starting  winding  is 
in  place.  This  winding  consists  of  four  coils  of  No.  n  wire,  each  having 

1 8  turns.     Each  of  these  coils  should  be  wound  into  the  proper  slots  over 


ONE-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR        137 


138 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


two  blocks  of  wood  (one  at  each  end  of 
the  core)  which  will  cause  the  coils  to 
project  i  in.  beyond  the  face  of  the 
stator  end  plates,  as  indicated  in  Fig. 
171.  After  they  are  wound  in  place, 
these  projecting  ends  are  to  be  bent 
upward  out  of  the  way  of  the  main 
coils,  which  must  be  wound  in  the  slots 
between  those  of  the  starting  winding. 
Fig.  172  indicates  this  bending  upward 
of  the  starting  coils,  and  also  shows  the 
slots  into  which  they  are  to  be  wound. 
They  are  connected  in  series  with  each 
other,  and  the  connections  must  be 
such  that  if  direct  current  were  passed 
through  this  winding  it  would  produce 
alternate  north  and  south  poles  within 
the  four  coils. 

After  the  starting  winding  is  in 
place  and  connected  up,  the  main  coils 
should  be  wound  into  their  slots;  two 
thicknesses  of  varnished  muslin  must  be 
laid  over  the  exposed  parts  of  the  start- 
ing winding  just  before  commencing 
the  winding  in  of  the  main  coils.  These 
main  coils  consist  each  of  36  turns  of 
No.  ii  double-cotton-covered  wire,  and 
each  coil  occupies  four  slots;  they  are 
to  be  wound  in  their  slots  as  indicated 
by  the  elementary  diagram,  Fig.  172. 
The  diagram  shows  only  one  turn  in 
each  slot,  but  the  reader  will  of  course 
understand  that  18  turns  are  to  be 
wound  in  the  inner  pair  of  slots,  /,  /, 
before  any  wire  is  wound  in  the  outer 
pair,  //,  //,  and  that  18  more  turns  are 
then  wound  into  these  latter  slots.  The 
coils  of  the  main  winding,  like  those  of 
the  starting  winding,  must  be  connected 
up  in  series  and  in  such  wise  that  direct 
current  passing  through  them  would  produce  four  magnetic  poles  of  alter- 
nate polarity;  north,  south,  north,  south.  It  makes  no  difference  what 


ONE-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR 


the  relation  is  between  the  direction  of  the  starting  coils  and  that  of  the 
main  coils;  the  terminals  must  be  carried  out  to  a  three-pole,  double- 
throw  knife-blade  switch,  as  indicated  in  Fig. 
173,  and  if  the  connections  at  first  made  do 
not  start  the  motor  in  the  direction  in  which 
it  is  intended  or  desired  to  run,  it  may  be  re- 
versed   by  merely   reversing   the   leads    from 
either  the  main  winding  or  the  starting  wind- 
ing, but  not  both. 

The  switch  should  be  mounted  so  that  the 
throw  is  horizontal  (unless  an  additional  main 
switch  is  provided),  in  order  that  it  may  be 
left  open  without  danger  of  accidentally  clos- 
ing by  gravity.  As  the  diagram  is  drawn, 
throwing  the  switch  to  the  left  puts  in  bolt 
windings,  for  starting  up;  when  the  machine 
attains  something  like  normal  speed,  the  switch 


FIG.  171 


To  Line 


should  be  thrown  quickly  to  the 
other  side,  leaving  only  the  main 
winding  in  circuit. 

If  the  builder  prefers  to  use 
simpler  apparatus,  two  ordinary 
double-pole  switches  may  be  used, 
one  for  the  main  winding  and  one 
for  the  starting  winding,  but  this 
arrangement  has  the  slight  disad- 
vantage that  the  user  may  close 
one  switch  and  leave  it  closed  for 
an  appreciable  length  of  time  be- 
fore closing  the  other,  which  might 
overheat  the  winding  thus  thrown 
in  alone,  as  the  motor  would  not 
start  up  and  the  winding  would 
be  provided  with  a  short-circuited 
secondary  —  the  rotor  conductors. 
The  result  would  be  similar  in 
kind,  though  less  in  degree,  to  that 
obtained  by  short-circuiting  the 
secondary  terminals  of  an  ordinary 
transformer  with  the  primary  con- 
nected to  the  supply  mains.  The 
motor  should  not  be  started  with 


140 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


any  load  on  it  except  the  countershaft  to  which  it  is  belted.  Even  with 
that  it  will  be  found  advisable  to  give  the  belt  a  strong  pull,  to  overcome 
standing  friction,  when  the  motor  is  thrown  into  circuit. 


FIG.  173 


CHAPTER  XVIII 
TWO-HORSE-POWER  SELF-STARTING   SINGLE-PHASE    INDUCTION   MOTOR 

THE  self-starting  induction  motor  herein  described  is  capable  of  giving 
two  brake  horse-power  on  a  single-phase  circuit  of  100  volts  and  125  to 
133  cycles.  The  speed  of  the  machine  will  depend,  of  course,  primarily 
upon  the  frequency  of  the  supply  current.  The  synchronous  speed  at 


iiiiiii.Hiimim»iiiiiiii|iiiiiii|iiiiiiiiiiii iiiiyiiiiiiiiiininiK 


FIG.  174 


FIG.  175 


125  cycles  is  2500,  and  at  133  cycles  it  is  2666  r.p.m.  The  actual  full- 
load  speed  will  be  something  like  2300  r.p.m.  at  125  cycles  and  about 
2640  r.p.m.  at  133  cycles. 

THE    STATOR 

Fig.  174  is  an  end  view  of  the  stator  and  Fig.  175  is  an  axial  section 

141 


142  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

of  it,  showing  the  arrangement  of  the  brass  end  plates  and  the  bolts  that 
hold  the  structure  together.  The  stator  core  is  built  up  of  270  discs  of 
sheet  steel,  each  20  mils  thick,  and  allowing  for  scale  and  irregularities 
the  mass  should  be  drawn  together  tightly  enough  to  make  the  axial  thick- 
ness 6  ins.  as  indicated  in  the  engraving.  The  stator  discs  are  9  ins.  in 
diameter  outside,  and  the  hole  in  the  center  is  6  9-16  ins.  in  diameter;  this 
latter  measurement  must  be  absolutely  exact.  The  36  slots  around  the 
edge  of  the  central  hole  are  to  be  punched  by  means  of  the  simple  punch 
and  die  shown  by  Fig.  176,  these  being  used  in  a  step-by-step  notching 
press.  It  is  not  assumed  that  the  builder  will  possess  one  of  these  presses 
or  buy  one  for  the  purpose  of  building  this  one  motor;  but  he  can  easily 
make  the  punch  and  die  and  have  the  work  done  at  some  shop  where  such 
presses  are  in  use. 

THE    PUNCH 

The  punch  is  built  up  in  three  pieces,  a  shank  and  holder  plate  of 
cast  iron,  a  punch  pad  of  ordinary  machine  steel,  and  the  punch  proper, 
of  annealed  steel.  The  punch  pad  is  a  simple  rectangular  plate  in  the 
center  of  which  is  worked  a  socket  for  the  punch,  the  outline  of  this  socket 
being  the  same  as  that  of  the  main  portion  of  the  opening  in  the  die.  The 
punch  is,  of  course,  of  the  same  outline  on  its  face  as  the  complete  opening 
in  the  die,  and  the  upper  part  of  it  is  to  be  made  a  very  snug  fit  in  the  hole 
in  the  punch  pad.  The  latter  is  secured  to  the  punch  holder  by  means  of 
four  J-in.  flat-head  machine  screws.  In  machining  the  holder,  great  care 
must  be  taken  to  have  the  face  of  it  absolutely  at  right  angles  with  the  axis 
of  the  shank.  The  wall  of  the  socket  in  the  punch  pad  must  also  be 
precisely  at  right  angles  with  the  face  that  matches  the  face  of  the  holder 
plate. 

Fig.  176  shows  the  punch  pad  partly  unscrewed  from  the  holder,  and 
the  punch  removed  from  its  socket;  it  is  held  in  the  socket  by  means  of 
J-in.  round-nosed  set-screw,  and  a  depression  should  be  machined  in  the 
side  of  the  punch  to  allow  the  nose  of  the  set-screw  to  seat  itself  without 
having  to  burr  the  punch.  After  the  punch  has  been  filed  to  shape,  it 
must  be  tempered.  In  first  hardening  it,  the  steel  should  be  heated  to  a 
bright  red  and  "quenched"  in  oil  or  lukewarm  water;  if  very  cold  water 
is  used  the  steel  will  be  too  brittle.  The  temper  should  be  drawn  in  the 
flame  of  a  Bunsen  burner,  and  the  steel  should  be  wiped  frequently  with 
an  oily  rag  during  the  heating.  If  the  reader  is  not  familiar  with  the  process 
of  "drawing"  the  temper  of  tool  steel,  he  had  better  get  this  done  by  an 
experienced  workman. 


TWO-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR 


THE    DIE 

The  die  is  to  be  made  of  annealed  steel,  of  the  quality  used  for  this 
class  of  work  (any  dealer  will  supply  the  proper  quality  if  told  what  it  is 
to  be  used  for).  The  sketches  show  clearly  the  shape  and  dimensions  of 
the  die.  The  dotted-line  arcs  indicate  the  inner  and  outer  edges  of  the 
stator  disc  when  in  position  for  punching.  The  hole  in  the  die  may  be 
most  readily  cut  by  first  drilling  two  holes  5-16,  in.  in  diameter  and  one 
hole  J  in.  in  diameter  along  a  straight  line  scribed  on  the  face  of  the  die 
block;  the  distances  from  center  to  center  of  these  holes  are  stated  in  the 
supplementary  sketch  between  the  plan  view  and  the  side  view  of  the  die. 


o 


r~ 


Preliminary  holes 


FIG.  176 

Having  drilled  these  three  holes,  the  superfluous  metal  must  be  filed 
away  slowly  and  very  carefully  until  the  desired  shape  of  slot  is  obtained. 
Then  the  hole  must  be  enlarged  on  the  under  side  of  the  die  block  in  order 
to  give  clearance  for  the  small  pieces  punched  out  of  the  stator  discs  to 
free  themselves. 

The  die  is  bolted  to  the  bolster  (which  need  not  be  made  by  the  amateur, 
as  the  shop  in  which  the  punching  is  done  will  have  bolsters  from  which  an 
appropriate  selection  may  be  made)  by  means  of  two  cap  screws  and  two 
flat-head  machine  screws.  The  cap  screws  also  hold  the  stripper  plate, 
which  is  a  rectangular  steel  plate  f  in.  thick  and  of  the  same  outline  as  the 
base  of  the  die  block ;  it  must  have  a  hole  cut  in  it  which  will  come  directly 
over  the  hole  in  the  die,  but  the  hole  in  the  stripper  need  not  be  accurately 
machined  to  the  shape  of  the  punch ;  it  may  be  a  simple  rectangular  aperture 


I44  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

f  in.  wide  and  i  in.  long.  After  the  hole  in  the  die  has  been  finished  to 
fit  snugly  about  the  punch,  which  must  touch  every  part  of  the  wall  of  the 
die  hole,  the  die  is  to  be  tempered.  The  remarks  concerning  the  tempering 
of  the  punch  apply  also  to  the  die. 

STATOR   CLAMPING   PLATES   AND   ASSEMBLY 

The  brass  end  plates  are  cast  with  the  slots  in  them,  the  sizes  of  the 
slots  in  these  plates  being  a  trifle  full,  as  compared  with  the  punched  slots 
in  the  core  discs.  It  will  not  do  to  use  a  simple  brass  ring  of  an  internal 
diameter  large  enough  to  clear  the  slots  in  the  core;  the  teeth  between 
these  slots  must  be  clamped  together  tightly  along  with  the  body  portion 
in  order  to  reduce  as  far  as  possible  the  humming  of  the  machine  when  in 
operation.  In  assembling  the  core  discs  between  the  brass  end  plates, 
the  structure  should  be  clamped  together  by  means  of  two  heavy  cast-iron 
discs  8  ins.  in  diameter  and  a  ij-in.  bolt  through  the  center;  this  work 
may  be  facilitated  greatly  by  the  use  of  ordinary  iron  clamps  such  as  are 
found  in  all  machine  shops,  applying  these  at  points  around  the  outer 
edge  of  the  stator  in  order  to  even  up  the  compression  and  assist  the  central 
clamping  bolt.  After  the  discs  are  drawn  to  position,  the  holes  near  the 
outer  edge  may  be  drilled;  if  the  brass  end  plates  have  been  made  of  a 
hard  alloy,  the  top  one  will  serve  as  a  jig  for  the  drill.  In  this  event  it 
should  be  drilled  before  assembling  the  core  discs,  but  the  under  plate 
should  be  left  undrilled;  when  the  discs  are  assembled,  the  holes  may  be 
drilled  clear  through  them  and  the  under  brass  plate.  A  much  safer  plan, 
however,  is  to  make  a  cast-iron  jig  plate  and  clamp  the  discs  between  it 
and  a  plain  cast-iron  plate  for  drilling ;  the  brass  end  plates  should  be 
drilled  by  the  same  jig  plate,  but  separately. 

JOURNAL   BRACKETS 

The  four  f-in.  bolts  which  hold  the  stator  core  together  do  not  in  this 
case  serve  to  hold  the  journal  brackets  or  end  caps  in  place.  Fig.  177 
shows  one  of  these  end  caps  and  an  axial  section  through  the  center  of  it. 
The  drawings  require  no  explanation  beyond  saying  that  the  caps  are  to 
be  made  of  cast  iron. 

The  journal  sleeves  shown  in  the  engraving  are  of  the  self-aligning 
type,  but  if  the  reader  is  not  very  skilful  at  machine  tool  work  it  will  be 
preferable  to  make  them  perfectly  straight,  making  the  outer  diameter  of 
the  sleeves  if  ins.  the  whole  length.  No  pulley  has  been  shown,  as  this 
can  be  bought  for  less  than  it  would  cost  an  amateur  to  make  it.  The 
proper  size  is  4  or  4^  ins.  in  diameter  at  the  crown  and  2  J  ins.  width  of  face. 

The  rotor  is  shown  by  Fig.  178.  It  consists  of  270  discs  of  sheet  steel 
20  mils  thick,  clamped  on  the  shaft  between  two  cast-brass  end  plates, 


TWO-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR         145 

which  also  serve  to  connect  the  ends  of  the  rotor  conductors.  There  are 
29  of  these,  each  f  in.  in  diameter  and  yj  ins.  long;  the  holes  in  the  rotor 
discs  are  13-32  in.  in  diameter,  and  may  be  drilled  with  the  aid  of  two  cast- 
iron  plates  between  which  the  discs  are  temporarily  clamped,  one  of  the 
cast-iron  plates  to  be  previously  drilled  so  as  to  serve  as  a  jig  for  the  drill 
when  the  discs  are  drilled. 


FIG.  177 


STATOR  WINDINGS 

After  the  stator  is  finished  the  slots  and  end  surfaces  of  the  core  should 
be  insulated  by  means  of  red  rope  paper  0.025  in.  (25  mils)  thick,  which 
should  be  thoroughly  varnished  with  shellac  before  being  put  in  place. 
The  main  stator  winding  must  not  be  put  on  until  the  starting  winding  is 
in  place.  This  winding  consists  of  six  coils  of  No.  8  wire,  each  having 
8  turns.  Each  of  these  coils  should  be  wound  into  the  proper  slots  over 
two  blocks  of  wood  (one  at  each  end  of  the  core),  which  will  cause  the 


146 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


coils  to  project  i  in.  beyond  the 
face  of  the  stator  end  plates,  as 
indicated  in  Fig.  179.  After  they 
are  wound  in  place,  these  pro- 
jecting ends  are  to  be  bent  up- 
ward out  of  the  way  of  the 
main  coils,  which  must  be  wound 
in  the  slots  between  those  of  the 
starting  winding.  Fig.  180  in- 
dicates this  bending  upward  of 
the  starting  coils,  and  also  shows 
the  slots  into  which  they  are  to 
be  wound.  They  are  connected 
in  series  with  each  other,  and  the 
connections  must  be  such  that 
if  direct  current  were  passed 
through  this  winding  it  would 
produce  alternate  north  and 
south  poles  within  the  six  coils. 
After  the  starting  winding  is 
in  place  and  connected  up,  the 
six  main  coils  should  be  wound 
into  their  slots;  two  thicknesses 
of  varnished  muslin  must  be  laid 
over  the  exposed  parts  of  the 
starting  winding  just  before 
commencing  the  winding  in  of 
the  main  coils.  These  main  coils 
consist  each  of  16  turns  of  No. 
8  double-cotton-covered  wire, 
and  each  coil  occupies  four  slots ; 
they  are  to  be  wound  in  their 
slots  as  indicated  by  the  ele- 
mentary diagram,  Fig.  180.  The 
diagram  shows  only  one  turn  in 
each  slot,  but  the  reader  will  of 
course  understand  that  8  turns 
are  to  be  wound  in  the  inner 
pair  of  slots,  7,  7,  before  any 
wire  is  wound  in  the  outer  pair, 
77,  77,  and  that  8  more  turns 
are  then  wound  into  these  latter 


TWO-HORSE-POWER  SELF-STARTING  INDUCTION  MOTOR 


147 


slots.  The  coils  of  the  main  winding,  like  those  of  the  starting  winding, 
must  be  connected  up  in  series  and  in  such  wise  that  direct  current 
passing  through  them  would  produce  six  mag- 
netic poles  of  alternate  polarity :  N,  S,  N,  S,  N,  S. 
It  makes  no  difference  what  the  relation  is 
between  the  direction  of  the  starting  coils  and 
that  of  the  main  coils;  the  terminals  must  be 
carried  out  to  a  three-pole,  double-throw  knife- 
blade  switch,  as  indicated  in  Fig.  181,  and  if 
the  connections  at  first  made  do  not  start  the 
motor  in  the  direction  in  which  it  is  intended 
or  desired  to  run,  it  may  be  reversed  by  merely 
reversing  the  leads  from  either  the  main  wind- 
ing or  the  starting  winding,  but  not  both. 

The  switch  should  be  mounted  so  that  the 
throw  is  horizontal  (unless  an  additional  main 
switch  is  provided),  in  order  that  it  may  be  left 

open  without  danger  of  accidentally  closing  by  gravity.     As  the  diagram  is 
drawn,  throwing  the  switch  to  the  left  puts  in  both  windings,  for  starting  up  > 


FIG.  i 80 


when  the  machine  attains  something  like  normal  speed,  the  switch  should  be 
thrown  quickly  to  the  other  side,  leaving  only  the  main  winding  in  circuit.- 


148 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


If  the  builder  prefers  to  use  simpler  apparatus,  two  ordinary  double-pole 
switches  may  be  used,  one  for  the  main  winding  and  one  for  the  starting 
winding,  but  this  arrangement  has  the  disadvantage  that  the  user  may 
close  one  switch  and  leave  it  closed  for  an  appreciable  length  of  time  before 
closing  the  other,  which  might  overheat  the  winding  thus  thrown  in  alone, 
as  the  motor  would  not  start  up  and  the  winding  would  be  provided  with 

To  Line 


f         0        = 

T 

—-    i  i  e   i 

T    4    e   i 

I 

1 

.^-TStartme    1 

FIG.  181 

a  short-circuited  secondary  —  the  rotor  conductors.  The  result  would  be 
similar  in  kind,  though  less  in  degree,  to  that  obtained  by  short-circuiting 
the  secondary  terminals  of  an  ordinary  transformer  with  the  primary 
connected  to  the  supply  mains.  The  motor  should  not  be  started  with 
any  load  on  it  except  the  countershaft  to  which  it  is  belted.  Even  with 
that  it  will  be  found  advisable  to  give  the  belt  a  strong  pull,  to  overcome 
standing  friction,  when  the  motor  is  thrown  into  circuit. 


CHAPTER  XIX 

ONE-KILOWATT  COMBINED  ALTERNATING  AND  DIRECT-CURRENT 

MACHINE 

THERE  are  presented  in  this  chapter  designs  and  working  drawings 
for  a  type  of  combined  alternating  and  current  machine  which  it  is  thought 
will  prove  generally  useful  for  experimental  and  laboratory  work  in  alter- 
nating and  direct  currents,  and  which  is  applicable  on  most  of  the  electric- 
lighting  circuits  found  in  practice. 

The  design  contemplates  working  the  machine  in  a  number  of  different 
ways: 

1.  As  a  direct- current  generator  or  motor. 

2.  As  a  single,  two,  or  three-phase  generator  or  motor. 

3.  As  a  rotary  converter,  changing  single,  two,  or  three-phase  currents 
to  direct  current. 

4.  As  an  inverted  rotary  converter,  changing  direct  current  to  single, 
two,  or  three-phase  alternating  currents. 

5.  As  a  phase  transformer,  changing  alternating  current  of  one  phase 
to  that  of  another  number  of  phases. 

Some  of  the  foregoing  functions  may  be  in  operation  at  the  same  time; 
for  instance,  Nos.  i  and  2  combined  would  give  a  "  double-current " 
generator.  Also  No.  3  or  No.  4  may  be  in  operation  simultaneously  with 
No.  5._ 

This  machine  is  designed  for  no  volts  direct  current,  and  either  80 
volts  single  or  two-phase  alternating,  or  70  volts  three-phase  alternating. 
These  voltages  admit  of  considerable  adjustment,  however,  by  varying 
the  field  excitation  or  speed  in  case  of  a  generator.  The  values  given 
represent  about  the  maximum  which  can  be  developed  continuously. 

In  operating  on  single-phase  alternating  circuits  it  is  necessary  to  adopt 
some  device  which  will  make  the  machine  self-starting,  and  this  has  been 
provided  in  the  shape  of  a  special  switch  located  in  the  base  of  the  machine 
and  which,  at  starting,  temporarily  changes  the  connections  to  those  of  a 
series  motor  which,  as  is  well  known,  readily  starts  when  alternating 
current  is  turned  on.  The  armature  is  allowed  to  reach  a  speed  slightly 

149 


150  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

above  synchronism,  and  the  switch  is  then  thrown  over  to  the  running 
position,  where  the  machine  operates  as  an  ordinary  synchronous  motor. 

In  starting  on  two  or  three-phase  circuits,  the  same  switch  is  utilized 
to  break  up  the  field  winding  into  a  number  of  short  sections  on  open 
circuit,  thereby  avoiding  the  high  induced  e.m.f.'s  which  would  otherwise 
be  produced  on  turning  the  alternating  current  into  the  armature  winding. 
It  will  be  understood  that  where  two  or  three-phase  currents  are  employed 
the  machine  is  self -starting  without  any  special  device,  by  virtue  of  the 
rotary  field  principle.  If  the  starting  current,  with  this  arrangement,  is 
found  to  be  objectionably  large,  it  can  be  avoided  by  starting  on  a  reduced 
pressure  supplied  from  small  auto-transformers. 

The  general  features  of  the  design  are  multipolar  field  having  a  circular 
yoke  of  cast  iron  with  laminated  wrought-iron  poles  cast  in.  This  type 
is  selected  because  it  admits  of  high  magnetic  density  and  short  air-gap, 
and  consequently  much  greater  output  than  does  an  all  cast  field,  while 
at  the  same  time  it  is  only  slightly  more  expensive  or  difficult  to  construct. 
An  all  cast-iron  field  of  the  same  general  design  will  have  only  a  little 
more  than  half  the  output,  and  an  all  cast-steel  field,  while  good  magneti- 
cally, is  scarcely  to  be  considered  at  present  owing  to  the  difficulty  in 
securing  reliable  steel  castings. 

Field  coils  are  wound  in  two  or  more  sections  each,  and  provided  with 
terminals  for  connection  to  the  starting  switch.  This  is  necessary  in  order 
to  obtain  a  sufficient  reduction  in  the  impedance  by  connecting  the  various 
sections  in  multiple  at  the  start. 

A  distributed  armature  winding  is  used,  with  collector  rings  tapped  in 
at  appropriate  intervals  on  the  commutator  for  alternate-current  working. 
The  toothed  armature  core  has  deep  and  narrow  slots,  and  is  provided  with 
a  formed-coil  winding,  as  in  direct-current  practice. 

The  minimum  number  of  slots  and  coils  is  determined  by  the  number 
of  poles  and  by  the  consideration  that  taps  must  be  made  for  both  two 
and  three-phase  working.  The  quotient  obtained  by  dividing  the  number 
of  coils  or  commutator  segments  by  the  number  of  poles  must  be  divisible 
by  two  for  two-phase  working  and  by  three  for  three-phase  working,  and 
hence  by  two  times  three  for  both  together.  Thus  24  coils  and  segments 
are  appropriate  for  a  four-pole  machine,  36  for  a  six-pole,  and  so  on. 

Six  collector  rings  will  be  required ;  ordinarily  seven  would  be  necessary, 
four  for  two-phase  and  three  for  the  three-phase.  By  making  one  of  the 
two-phase  rings  the  starting  point  for  the  three-phase,  one  ring  serves  for 
two,  and  the  total  number  may  be  reduced  to  six. 

It  would  be  possible,  of  course,  to  use  but  four  rings,  obtaining  three- 
phase  current  by  means  of  two-phase  -  three-phase  transformers,  but  it  is 
preferable  to  add  two  rings  and  obtain  all  phases  directly  from  the  machine. 


ONE-KILOWATT  COMBINED  ALTERNATING  MACHINE  151 

The  hollow  base  plate,  which  is  cast  in  one  piece  with  the  bearing 
pedestals,  serves  as  a  housing  for  the  starting  switch  already  referred  to. 
This  switch  is  operated  by  a  lever  on  the  outside,  at  the  front  or  direct- 
current  end  of  the  machine,  and  has  two  positions  120  degrees  apart,  the 
starting  and  running  positions  respectively.  In  the  starting  position  the 
various  sections  of  the  field  winding  are  in  parallel  with  each  other  and 
in  series  with  the  direct-current  end  of  the  armature. 

In  the  running  position  the  field  sections  are  in  series,  giving  the  maxi- 
mum resistance,  and  are  placed  across  the  direct-current  brushes  at  the 
same  time  alternating  current  from  the  single-phase  mains  is  turned  into 
the  collector  rings. 

A  pulley  having  a  heavy  rim  for  the  purpose  of  securing  a  considerable 
fly-wheel  effect  will  be  found  advantageous  in  adding  to  the  smooth  running 
of  the  machine,  particularly  when  used  as  a  rotary  from  the  alternating- 
current  end. 

A  pulley  of  this  kind  will  also  be  useful  where  the  machine  is  to  be 
used  as  a  generator  direct  belted  to  a  gas  or  gasoline  engine.  The  need 
for  a  considerable  amount  of  momentum  in  the  running  parts  of  a  rotary 
is  real  and  genuine,  for  without  it  there  is  a  disagreeable  oscillation  or 
''pumping,"  which  makes  synchronism  unstable  and  sometimes  causes 
the  machine  to  break  out  of  step  even  before  full  load  is  reached. 

The  bearings  are  of  the  ring-oiling  type,  and  of  a  form  which  gives 
good  lubrication  without  the  disadvantage  of  having  oil  thrown  off  outside 
the  bearing. 

The  running  qualities  of  these  machines  will  doubtless  prove  quite 
satisfactory.  There  is  not  likely  to  be  trouble  from  sparking,  in  spite  of 
the  fact  that  the  armature  is  multiple  wound,  in  which,  ordinarily,  a  slight 
lack  of  symmetry  in  field  strength  would  cause  heating  and  sparking. 
The  connections  already  made  to  the  collector  rings  for  another  purpose 
serve  also  as  equalizers,  which  permit  equalizing  currents  to  flow  and 
thus  counteract  any  slight  inequality  in  the  various  field  poles. 

Armature  reaction  may  be  guarded  against  by  clipping  off  the  corners 
of  every  third  lamination  of  the  field  poles.  This  will  have  the  effect  of 
increasing  the  density  in  the  pole  tips  to  practical  saturation,  thus  avoiding 
further  distortion  by  armature  currents  and  giving  practically  a  fixed 
point  of  commutation  for  all  loads. 

Heating  in  the  armature  and  field  windings  should  not  prove  serious, 
for  the  current  densities  employed  are  moderate,  considering  the  size  of 
machine.  In  the  pole-pieces,  heating  would  ordinarily  be  expected,  due 
to  the  short  air-gap  and  hign  density,  but  their  laminated  construction  will 
entirely  obviate  this  difficulty. 

While  primarily  intended  for  use  on  i25-cycle  circuits,  modifications 


152  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

will  be  indicated  enabling  these  machines  to  be  used  on  6o-cycle  circuits 
also.  This  involves  either  a  reduction  in  speed  of  one  half,  with  a  corre- 
spondingly reduced  output  and  voltage,  or  a  reduction  in  the  number  of 
poles  to  one  half,  keeping  the  speed  and  output  the  same,  but  necessitating 
a  somewhat  more  difficult  change  in  connections  and  winding. 


FIG.  182 


Referring  now  to  the  one-kilowatt  machine,  Fig.  182  shows  an  end 
view  of  the  field  magnet  and  base.  There  are  four  poles  cast  into  the 
yoke,  which  forms  a  separate  casting  and  is  bolted  to  the  base  plate  by 
four  y-i6-in.  by  ij-in.  hexagon  cap  screws.  The  poles  are  built  up  of 


ONE-KILOWATT  COMBINED  ALTERNATING  MACHINE  153 

plain  rectangular  strips  of  soft  iron  about  No.  22  gage,  which  are  clamped 
between  two  heavier  plates  by  one  or  more  long  flat-head  bolts. 

The  pattern  for  the  field  casting  should  be  made  just  as  though  it 
were  for  an  all  cast  field,  the  laminated  pole-pieces  being  laid  in  the  mold 
after  the  pattern  has  been  drawn,  and  the  iron  poured  in  around  them. 
The  natural  shrinkage  of  the  metal  on  cooling  will  cause  the  poles  to  be 
tight  and  secure.  It  would  give  additional  security,  iowever,  to  notch  the 
poles  before  casting  in  as  indicated  by  the  dotted  lines.  Still  another  plan 
is  to  leave  the  end  plates  short,  and  to  spread  the  laminations  apart  where 
they  enter  the  yoke.  This  will  allow  the  iron  to  fill  in  the  interstices  and  so 
obtain  a  good  hold  on  the  pole.  As  the  poles  have  been  left  with  square 
ends,  they  must  now  be  bored  out  35-16  ins.,  and  the  corners  slightly  rounded. 

Fig.  183  is  a  longitudinal  half  section  of  the  assembled  machine,  which 
shows  the  construction  of  the  armature,  bearings,  commutator,  and  col- 
lector rings,  and  also  the  location  of  the  starting  switch  in  the  base. 

The  armature  core  is  built  up  of  soft  steel  discs  about  No.  27  gage; 
two  heavier  discs  of  wrought  iron,  3-16  in.  thick,  are  provided  at  the  ends 
as  a  reinforcement  for  the  teeth,  and  the  whole  is  clamped  between  two 
cast-iron  flanges  run  up  on  threads  cut  in  the  shaft.  These  flanged  pieces 
serve  also  as  a  support  for  the  "  straight-out "  winding. 

Plain  round  discs  may  be  used  in  building  the  core  and  the  slots  milled 
out,  being  careful,  however,  to  take  the  discs  apart  after  milling  and 
insulate  them  with  paper  or  japanning.  The  keyway  in  the  disc  insures 
their  registering  when  reassembled,  in  spite  of  possible  slight  inaccuracy 
in  milling  the  slots.  It  is  not  necessary  to  insulate  the  discs  from  the  shaft 
if  they  are  fairly  well  insulated  at  all  other  points. 

The  bearings  have  a  central  rib  f  in.  thick,  which  supports  the  brass 
or  bronze  sleeve  forming  the  journal  proper.  The  oil  pockets  at  either 
side  of  the  web  communicate  by  means  of  a  slot  cored  out  in  the  web,  so 
that  the  oil  level  may  remain  the  same  on  each  side.  The  oil  rings  are 
J  in.  wide  and  ride  on  the  shaft  through  grooves  turned  eccentrically  in 
the  sleeve. 

The  commutator  has  a  steel  sleeve  fitting  the  shaft,  upon  which  are 
two  flanges,  one  solid  with  the  sleeve  and  the  other  threaded  on  it  and 
tightened  by  means  of  a  spanner  wrench  applied  to  holes  drilled  in  its 
face.  Both  flanges  are  undercut  at  an  angle  of  about  60  degrees,  to  hold 
the  segments  in  place. 

Probably  the  best  way  to  construct  the  commutator  is  to  turn  up  a 
copper  casting  of  the  required  section,  and  then  slit  the  cylinder  into  24 
segments  by  means  of  a  i-32-in.  cutter,  in  a  milling  machine.  The  seg- 
ments are  then  built  up  with  i-32-in.  mica  between,  and  insulated  from 
the  sleeve  by  1-16  in.  of  mica  or  other  good  Insulation. 


154 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


ONE-KILOWATT  COMBINED  ALTERNATING  MACHINE 


The  collector  rings  are  similar  in  construction.  The  two  end  rings 
are  counter-bored  to  let  in  the  flanges  of  the  sleeve,  which,  in  this  case, 
need  not  be  undercut.  The  other  rings  are  plain  round  and  are  simply 
slipped  over  the  insulating  sleeve,  and  separated  from  each  other  by 
i-i6-in.  fiber,  or  equivalent  insulation,  which  is  allowed  to  project  some- 
what above  the  surface  of  the  rings. 

Connections  to  the  rings  are  made  by  drilling  in  from  the  back  side 
and  soldering  in  short  wires,  No.  12  or  No.  14,  which  should  be  carefully 
insulated  where  they  pass  through  other  rings  by  small  fiber  or  rubber 
tubes.  These  wire  leads  are  made  only  just  long  enough  to  project  a 
short  distance  from  the  back  ring,  and  are  there  soldered  to  some  thin 
copper  strips  taped  and  laid  in  the  bottom  of  the  armature  slots,  six  of 
which  have  been  cut  1-16  in.  deeper  than  the  rest  to  accommodate  these 
connections.  It  will  be  the  more  convenient  to  make  all  these  connections 
permanently  and  test  them  before  laying  on  the  armature  coils. 


FIG.  184 


FIG.  186 


Fig.  184  shows  the  brush  ring  for  the  alternating-current  end,  and 
Fig.  185  the  one  for  jthe  direct-current  end  of  the  machine.  They  are 
made  in  halves,  held  together  by  screws,  which  will  facilitate  in  assembling 
the  machine.  The  direct-current  ring  has  four  lugs  for  supporting  the 
brush-holder,  and  the  alternating-current  ring  has  six,  one  for  each  of  the 
six  collector  rings. 

Fig.  1 86  shows  an  end  view  of  the  armature  core  and  Fig.  187  a  develop- 
ment of  the  armature  winding.  The  core  has  24  slots  3-16  in.  wide  and 
7-16  in.  deep.  Every  fourth  slot  is  made  J  in.  deep  to  allow  space  for 
connections  to  the  rings.  The  teeth  are  plain  straight  and  the  armature 
must  be  banded  after  the  coils  are  in  place. 

The  armature  winding  is  of  the  type  known  as  " straight  out"  and  is 
composed  of  form- wound  coils  of  No.  20  double-cotton-covered  wire,  each 
coil  consisting  of  16  turns  arranged  4  wide  and  4  deep.  The  coil  is 
wound  as  a  simple  straight  loop,  and  after  receiving  a  wrapping  of  tape  it 
is  bent  until  it  will  span  one  quarter  of  the  armature  circumference.  One 


156 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


side  of  a  coil  occupies  the  top  of  a  slot,  and  the  other  side  of  the  same  coil 
occupies  the  bottom  half  of  a  slot  90  degrees,  or  six  slots,  in  advance  of  the 
first.  Thus  arranged,  the  coils  interleave  in  a  very  compact  mannner  and 
the  space  required  for  cross  connection  is  reduced  to  a  minimum. 

The  terminals  are  brought  out  at  the  apex  of  the  coil  and  are  connected 
directly  to  the  commutator  segments,  the  beginning  of  one  coil  and  the 
ending  of  the  adjacent  coil  connecting  to  the  same  segment.  The  advan- 
tage in  bringing  the  terminals  straight  out  to  the  commutator  in  this  way 
is  that,  in  addition  to  being  more  convenient,  it  permits  the  brushes  to  be 
placed  opposite  the  poles,  where  they  are  more  accessible  than  when 
placed  between  the  poles. 

Fig.  1 88  shows  details  of  the  brush-holders.  The  direct-current  holders 
are  of  simple  construction,  but  neat  in  appearance,  and  are  intended  for 
radial  graphite  or  carbon  brushes  f  in.  thick,  ij  ins.  wide,  and  i  in.  long. 


FIG.  187 


FIG.  i 88 


The  necessary  tension  on  the  brush  is  supplied  by  an  open- coil  spring 
concealed  in  a  hollow  lug  cast  on  the  side  of  the  holder,  and  acting  on  a 
small  pressure  foot  shown  separately  in  the  drawings.  By  lifting  the  pres- 
sure foot  by  means  of  the  eye  "at  its  top  and  turning  it  half  around,  a  brush 
may  be  readily  removed  from  or  inserted  into  the  holder. 

The  alternating-current  brush-holders  are  carried  upon  studs  supported 
from  the  brush  ring,  and  have  slots  J  in.  by  f  in.  for  copper-leaf  brushes. 
There  need  not  be  any  spring  tension  provided,  as  the  natural  spring  of 
the  brush  will  be  sufficient  to  insure  good  contact.  Two  thumb  screws 
are  provided,  one  to  hold  the  brush  and  the  other  to  clamp  the  holder 
upon  its  stud  in  the  desired  position.  The  studs  are  of  different  lengths, 
the  dimension  marked  X  having  the  values  3^  ins.,  2f  ins.,  2^  ins.,  if  ins., 
ij  ins.,  and  f  in.  for  the  six  studs.  Quarter-inch  brass  rod  may  be  used 
to  make  these  from,  the  collars  being  soldered  or  threaded  on  and  the  ends 


ONE-KILOWATT  COMBINED  ALTERNATING  MACHINE 


I57 


threaded  for  a  hexagon  nut.     All  brush-holders  and  parts  should  be  made 
in  brass  or  bronze. 

Figs.  189  and  190  are  diagrams  to  be  followed  in  making  taps  to  the 
collector  rings.  The  four-pole  arrangement,  Fig.  189,  is  intended  for  oper- 
ating on  i25-cycle  circuits,  and  the  two-pole,  Fig.  190,  for  60  cycles.  These 
connections  should  be  made  at  the  back  of  the  commutator  before  it  is 
placed  in  position  on  the  shaft.  In  the  four-pole  arrangement,  for  instance, 
segments  No.  i  and  No.  13  are  connected  together  and  to  a  lead  marked 
No.  i,  which  goes  to  collector  ring  No.  i,  and  similarly  for  the  others. 
Thus  connected,  single-phase  current  may  be  obtained  from  rings  1-2  or 
3-4.  Two-phase  current  from  1-2  and  3-4  and  three-phase  current  from 
1-5-6.  The  output  and  voltage  with  these  various  connections  are  as 
follows:  Direct  current,  10  amperes  at  no  volts;  single-phase  alternating, 


FIG.  189 


FIG.  190 


10  amperes  at  80  volts;  two-phase  alternating,  7  amperes  per  phase  at 
80  volts;  three-phase  alternating,  6  amperes  per  phase  at  70  volts. 

Fig.  191  shows  a  form  of  fly-wheel  pulley  which  is  recommended  as 
conducing  to  smooth  running,  for  reasons  already  referred  to.  This 
pulley  is  of  cast  iron  and  should  be  turned  perfectly  true  all  over  and 
carefully  balanced,  as  should  also  the  armature.  These  rotating  parts 
will  be  required  to  run  at  3750  r.p.m.  on  125  cycles,  and  unless  precautions 
are  taken  the  vibration  will  be  excessive. 

Fig.  192  is  a  detail  of  the  armature  shaft.  This  is  designed  to  be 
turned  from  a  piece  of  f-in.  cold-rolled  steel,  and  for  this  reason  the  cus- 
tomary collar  at  one  end  has  been  omitted,  and  instead  threads  are  cut 
on  both  ends  for  receiving  the  end  plates  of  the  core.  This  does  away 
with  expensive  forgings  and  provides  a  shaft  requiring  only  a  minimum 
amount  of  turning.  Small  grooves  are  provided  at  the  journals  which 
prevent  oil  from  creeping  along  the  shaft  and  being  thrown  off  outside  the 
bearing.  There  are  two  keys  on  the  shaft,  one  for  the  core  punchings  and 
the  other  to  hold  on  the  pulley. 

Fig.  193  shows  the  arrangement  of  the  switch  cylinder  and  contacts 


158 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


for  the  single-phase  starting  device.  There  are  30  contact  fingers,  each 
5-16  in.  wide,  fastened  to  a  strip  of  fiber  \  in.  thick,  which  in  turn  is  screwed 
to^the  under  side  of  the  cast-iron  base  of  the  machine.  Upon  a  cylinder 
of  hard  wood  or  fiber  ij  ins.  in  diameter  are  arranged  two  rows  of  brass 
pieces,  sunk  in  grooves  cut  on  the  cylinder  and  upon  which  the  stationary 
contact  fingers  press. 

The  cylinder  may  be  rotated  through  an  angle  of  1 20  degrees  by  means 
of  a  handle  on  the  outside.  The  contacts  on  the  cylinder  are  120  degrees 
apart,  which  allows  sufficient  space  for  the  first  set  to  leave  contact  before 
the  second  comes  into  contact,  this  being  essential  to  avoid  short  circuit. 


FIG.  191 


FIG.  194 

Fig.  195  shows  a  diagram  of  connections 
for  the  starting  switch,  by  means  of  which 
its  action  may  be  readily  traced  out.  Num- 
bers 1-12  represent  the  sectional  field 
winding,  there  being  four  coils,  each  of 
which  is  wound  in  three  sections  of  ap- 
proximately equal  resistance.  There  are 


then  twelve  pairs  of  ends  which  lead  down  into  the  base  of  the  machine 
and  are  connected  to  the  stationary  contact  pieces,  which  are  represented 
by  the  upper  row  of  small  circles.  The  remaining  three  pairs  of  contacts 
connect  to  the  direct-current  brush  leads,  the  single-phase  rings,  and  the 
single-phase  mains,  respectively. 

The  lower  rows  of  circles  represent  the  contact  pieces  mounted  on  the 
cylinder,  and  these  are  connected,  as  here  indicated,  by  means  of  wires 
laid  in  grooves  upon  the  cylinder  and  occupying  that  portion  of  the  cylinder 
over  which  the  contact  fingers  do  not  pass. 


ONE-KILOWATT  COMBINED  ALTERNATING  MACHINE 


I59 


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DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


To  operate  the  machine  at  no  volts  direct  current  or  i25-cycle  alter- 
nating, no  changes  are  necessary.  For  6o-cycle  alternating,  however,  the 
number  of  poles  is  reduced  one  half  by  reversing  the  terminals  of  any  two 
successive  field  coils,  and  the  armature  winding  must  be  changed  to  a 
bipolar  one. 

Another  plan  is  to  reduce  the  speed  one  half,  thus  halving  the  voltage 
and  output  and  connecting  the  field  coils  in  series- multiple  so  that  they 
will  still  take  the  same  current  as  at  the  higher  voltage.  In  operating  the 
machine  as  a  converter,  if  it  is  desired  that  the  direct-current  output  be 
at  no  volts,  the  single  or  two-phase  input  must  be  at  80  volts.  This 
relation  of  voltage  is  fixed  and  can  be  expressed  by  direct-current  volts 
X  .707  =  alternating  volts,  and  for  three-phase  by  direct-current  volts 
X  .612  =  alternating-current  volts.  So  that  if  the  alternating  circuit  is 
of  52  or  104  volts  the  machine  should  be  supplied  at  the  proper  voltage 
through  a  transformer.  An  old  15-light  transformer  will  serve  for  this 
purpose,  and  it  should  be  arranged  so  that  its  secondary  voltage  can  be 
varied  to  some  extent  by  changing  the  number  of  secondary  turns  in 
circuit,  thus  giving  a  means  of  adjusting  the  direct-current  voltage. 

The  following  is  a  brief  summary  of  the  data  for  winding  and  general 
dimensions,  and  shows  the  method  of  calculating  same: 

Four-pole  machine,  3750  r.p.m. ;  armature,  3^  ins.  diameter,  3  ins. 
long;  24  slots,  3-16  in.  wide,  7-16  in.  deep;  total  number  of  conductors, 
768;  24  coils,  No,  20  wire,  4  wide,  4  deep;  No.  20  has  1021  circ.  mils, 
diameter  d.c.c.,  .042  in.;  direct-current  output  at  400  c.m.  per  ampere, 

jo  amperes;  useful  lines  per  pole  — — - —  =  240,000;  total  lines,  330,000. 


Part 

Material 

Total  lines 

Cross  sect. 

B. 

H. 

L. 

Amp.  turns 

Armature 

Wrought  iron 

120,000 

2.25  sq.  ins. 

53>3°° 

14 

1.4    in. 

20 

2  air-gaps 

Air 

240,000 

4-5 

53>3°° 

16,800 

.06  " 

I,OOO 

4  teeth 

Wrought  iron 

240,000 

2. 

120,000 

180 

•45   " 

80 

2  cores 

Wrought  iron 

330,000 

3-75 

88,000 

20 

i-5 

3° 

i  yoke 

Cast  iron 

1  65  ,000 

4- 

41,300 

74 

4-25  " 

3*5 

Total.  . 


144= 


The  table  above  gives  a  total  of  1445  ampere-turns  or  725  ampere-turns 
per  coil;  mean  length,  i  turn,  u  ins. 

n  X  n  X  725 

Circ.  mils  in  shunt  wire  -  -  =  290. 

25X12 

Use  No.  25  wire,  320  c.m.,  .028  in.  d.c.c.  1155  turns  (approximate) 
per  coil;  25  layers,  45  turns  wide. 


ONE  KILOWATT  COMBINED  ALTERNATING  MACHINE  161 

Wind  in  three  sections.     Bring  out  terminals  from  each  section. 

Resistance  of  shunt  field  = - —  =136  ohms. 

1000  X  1 2 

Normal  shunt  current,  .63  ampere.     Use  a  rheostat  of  about  50  ohms 
total  resistance  in  shunt-field  circuit. 

Weight  of  wire  in  shunt  coils  = —  =4.1  pounds. 

1000  X  12 

Length  of  wire,  each  armature  coil  =i6Xi3_ 

Total  length  of  wire,  armature,  =  24  X  17.4  =  417  feet. 
Total  weight  of  armature  wire  = — —  =1.3  pounds. 

IOOO 

417  X  10.1 

Resistance  of  armature  = =  .26  ohm. 

1000  X  16 

Drop  in  armature  at  full  load  =  10.63  X  «2^  =  2-7^ 


CHAPTER  XX 

TWO-KILOWATT  COMBINED  ALTERNATING  AND  DIRECT-CURRENT 

MACHINE 

The  2-kilowatt  machine  shown  in  the  accompanying  drawings  is 
similar  in  design,  construction,  and  operation  to  the  four-pole  machine 
described  in  the  preceding  chapter.  The  present  machine  is  somewhat 
larger,  runs  at  a  slower  speed,  and  has  about  double  the  output  capacity 
of  the  four- pole  machine.  Fig.  196  gives  an  end  view  of  the  field-magnet 
frame.  There  are  six  poles  of  laminated  iron  cast  into  a  circular  yoke  of 
cast  iron,  which,  in  turn,  is  bolted  to  the  base  plate  by  four  hexagon  cap 
screws.  After  the  poles  are  cast  in  and  it  is  seen  that  all  of  them  are 
tight  and  firm  in  the  yoke,  they  may  be  bored  out  to  the  proper  diameter, 
4.04  ins.  The  armature  is  to  be  finished  4  ins.  in  diameter,  so  that  the 
air-gap  will  be  .02  in.  across  at  each  pole;  this  will  be  ample  for  clearance 
if  care  is  taken  in  lining  up  the  machine. 

Fig.  197  is  a  section  of  the  assembled  machine  which  shows  the  con- 
struction and  relation  of  the  various  parts.  The  armature  is  of  the  usual 
laminated  construction,  the  core  discs  being  held  between  two  cast-iron 
flanges  screwed  upon  the  shaft.  If  the  armature  slots  are  milled  out,  the 
discs  must  be  taken  apart,  cleaned  up,  and  insulated  before  being  finally 
assembled  on  the  shaft.  If  this  is  not  done  the  eddy  current  loss  will  be 
excessive,  causing  heating  and  seriously  reducing  the  available  output. 
Fig.  198  shows  a  detail  of  the  armature  shaft.  This  is  intended  to  be 
made  from  i-in.  cold-rolled  steel.  Threads  are  cut  at  both  ends  of  the 
core  portion  to  receive  the  cast-iron  flanges  which  clamp  the  core  punchings. 
Two  keys  are  provided,  as  shown  in  the  drawing. 

The  bearings  are  made  with  a  brass  sleeve  fitting  the  shaft,  supported 
at  its  center  by  a  projecting  web  cast  in  the  bracket.  Although  it  is  pref- 
erable to  bore  the  bracket  for  this  sleeve,  the  machine  work  may  be  avoided 
by  coring  the  bracket  somewhat  larger  and  then  babbitting  the  sleeve  into 
its  support  when  the  parts  have  been  lined  up  in  their  proper  position. 
The  oil  rings  are  of  brass  f  in.  wide  and  i  J  ins.  inside  diameter;  grooves 

162 


TWO-KILOWATT  COMBINED  ALTERNATING  MACHINE 


'63 


are  cut  eccentrically  in  the  sleeves  to  receive  the  rings,  the  grooves  being 
made  about  5-32  in.  wide  in  order  to  allow  the  ring  a  small  amount  of  play. 
The  commutator  is  built  up  on  a  machine  steel  sleeve,  with  the  flanges 
undercut  at  60  degrees.  The  segments  may  be  cast  separately  or  cast  as 
a  solid  cylinder  and  afterward  cut  into  segments  on  a  milling  machine. 
The  segments  should  be  of  copper,  with  i-32-in.  mica  between  them, 


FIG.  196 

and  i-i6-in.  micanite,  or  equivalent  insulation,  between  the  sleeve  and 
segments.  The  number  of  segments  is  36.  The  collector  rings  are  six  in 
number  and  mounted  upon  a  sleeve  with  3-32^11.  fiber  discs  between  the 
rings.  Connections  are  made  by  drilling  in  from  the  back  and  soldering 
in  short  leads  of  No.  8  or  No.  10  wire,  one  to  each  ring.  Each  of  the 
leads  must  be  carefully  insulated  from  all  rings,  except  the  particular  one 


1 64 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 
-.?£- 


TWO-KILOWATT  COMBINED  ALTERNATING  MACHINE 


165 


to  which  it  is  electrically  connected.  Some  thin  copper  strips  are  to  be 
provided  with  a  wrapping  of  tape  and  laid  in  the  bottom  of  the  armature 
:slots,  six  of  which  must  be  made  1-16  in.  deeper  than  the  rest  to  accom- 
modate the  strips.  These  strips  carry  the  current  across  the  armature 
and  are  connected  to  the  commutator  at  the  proper  intervals. 

At  the  alternating- current  end  of  the  machine  the  fly-wheel  pulley  is 
.shown  in  position  on  the  shaft.  This  style  of  pulley  will  be  found  advan- 
tageous in  operating  the  machine  as  a  rotary  converter  or  in  driving  it  by 
means  of  a  gas  engine.  If  the  machine  be  used  as  a  motor  an  ordinary 
pulley  will  answer.  The  pulley  is  for  a  2j-in.  belt,  and  is  3!  ins.  in 
diameter. 

Fig.  199  shows  the  brush-holder  collar.  This  answers  for  both  the 
alternating-current  and  the  direct-current  ends  of  the  machine,  as  there 
are  six  collector  rings  and  also  six  brush-holders.  Care  should  be  taken 
in  drilling  the  holes  for  brush-holders  to  have  them  equidistant,  for 


FIG.  199 


FIG.  200 


upon  this  the  accuracy  in  spacing  the  brushes  around  the  commutator 
depends.  At  the  alternating-current  end  this  does  not  matter  particularly. 
The  brush-holder  collars  are  necessarily  made  in  halves,  as  it  would  be 
difficult  to  assemble  the  machine  with  a  one-piece  collar. 

Fig.  200  shows  details  of  the  brush-holders.  These  are  of  the  same 
type  as  those  already  described  in  connection  with  the  four-pole  machine. 
The  alternating- current  brush-holders  have  no  spring  tension  and  are 
designed  for  leaf-copper  brushes  J  in.  thick  and  f  in.  wide.  The  studs 
are  of  different  lengths  to  suit  the  position  of  the  rings;  the  dimension,  X, 
is  3!  ins.,  2|  ins.,  2\  ins.,  if  ins.,  i  3-16  ins.,  and  11-16  in.  for  the  six 
studs.  They  are  made  of  5-i6-in.  brass  rod.  The  direct-current  brush- 


1 66 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


holders  are  designed  for  radial  carbon  brushes  f  in.  thick,  ij  ins.  wide, 
and  i$  ins.  long. 

Fig.  201  is  an  end  view  of  the  armature  core.  There  are  36  slots, 
each  3-16  in.  wide  and  7-16  in.  deep;  every  sixth  slot  is  made  J  in.  deep 
to  allow  space  for  the  connection  strips  referred  to  above.  After  the  coils 
are  in  place  the  armature  must  be  banded  at  three  points,  one  band  to  go 
around  the  center  of  the  core,  and  one  around  each  end  of  the  winding 
where  it  projects  beyond  the  core.  A  groove  must  be  turned  in  the  pe- 
riphery of  the  core  to  accommodate  the  central  band,  so  that  the  thickness 
of  the  band  will  not  be  added  to  the  length  of  the  air-gap.  This  groove 
may  be  turned  on  the  core  before  the  slots  are  milled  out,  or  it  may  be 
done  afterward  by  filling  in  the  slots  temporarily  with  hard  wood  strips. 
It  should  be  about  1-16  in.  deep  and  f  or  7-16  in.  wide. 


J--H 


^ 


FIG.  201 


FIG.  202 


Fig.  202  shows  a  development  of  the  armature  winding.  This  is  of 
the  "  straight-out "  type,  and  is  composed  of  36  form- wound  coils  of  No.  20 
wire,  16  turns  per  coil.  One  side  of  a  coil  occupies  the  top  half  of  slot 
No.  i,  and  the  other  side  of  the  same  coil  occupies  the  bottom  of  slot  No. 
7;  that  is  to  say,  each  coil  spans  one  sixth  of  the  circumference  of  the  core. 
The  terminals  are  brought  out  at  the  apex  of  the  coil,  and  each  is  connected 
to  the  nearest  commutator  segment;  the  inside  terminal  of  one  coil  and 
the  outside  terminal  of  the  adjacent  coil  connect  to  the  same  segment. 
The  point  of  commutation  will  be  found  at  or  near  the  center  line  of  the 
pole-pieces. 

Fig.  203  is  a  diagram  of  the  connections  for  the  collector  rings.  This 
arrangement  is  for  a  six-pole  field.  The  leads  numbered  i  to  6  pass  across 
the  armature  and  are  connected  to  the  six  collector  rings  at  the  alternating- 
current  end  of  the  machine.  Connected  in  this  way,  single-phase  current 
may  be  obtained  from  rings  i  and  2  or  3  and  4,  two-phase  currents  from 
rings  i  and  2  and  3  and  4,  and  three-phase  currents  from  rings  1,5,  and  6. 


TWO-KILOWATT  COMBINED  ALTERNATING  MACHINE 


167 


The  output  and  voltage  with  each  of  these  various  methods  of  working 
•are  as  follows:  Direct  current,  15  amperes  at  115  volts;  single-phase  alter- 
nating, 15  amperes  at  80  volts;  two-phase  alternating,  n  amperes  per 
phase  at  80  volts;  three-phase  alternating,  9  amperes  per  phase  at  70  volts. 

Fig.  204  shows  the  outline  of  one  of  the  field  coils.  These  are  wound 
on  a  form,  and  each  coil  is  divided  into  two  sections  of  approximately 
equal  resistance,  with  separate  terminals  brought  out  from  each  section. 
The  size  of  wire  is  No.  23,  B.  &.  S.  gage. 

The  arrangement  employed  for  starting  the  machine  as  a  motor  on 
single-phase  circuits  is  as  shown  in  the  description  of  the  four-pole  machine 
(see  Figs.  193  and  195,  and  the  description  on  pages  157  and  158,  with  the 
single  exception  that  in  the  present  machine  there  are  six  coils  of  two 
sections  each  instead  of  four  coils  of  three  sections  each. 


FIG.  203 


FIG.  204 


To  operate  the  machine  at  no  volts,  direct-current,  or  125  cycles 
alternating,  the  speed  should  be  2500  r.p.m.  For  60  cycles  the  only 
method  available  is  to  reduce  the  speed  to  1200  r.p.m.  and  to  connect  the 
field  winding  in  series  multiple.  This  is  most  conveniently  done  at  the 
starting  switch  by  changing  the  wiring  of  the  last  row  of  contacts  on  the 
switch  cylinder,  so  that  when  the  switch  is  in  the  running  position  the  two 
sections  of  each  field  coil  will  be  in  multiple  and  the  six  multipled  pairs 
in  series  and  connected  across  the  direct-current  brushes.  This  will 
reduce  the  voltage  to  about  one  half  of  its  value  at  the  higher  speed,  and 
the  output  will  then  be  as  follows:  Direct-current,  15  amperes  at  55  volts; 
single-phase,  15  amperes  at  40  volts;  two-phase,  n  amperes  at  40  volts; 
three-phase,  9  amperes  at  35  volts.  It  is  probable  that  by  adjusting  the  field 
excitation,  the  voltage  could  be  brought  up  to  45  or  47  volts,  and  thus  ad- 
mit of  working  directly  on  single-phase  circuits  of  50  or  52  volts  as  a 
motor  or  rotary  without  the  use  of  an  individual  transformer.  For  other 
voltages  a  transformer  will  be  necessary. 


i68 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


The  following  is  a  summary  of  the  data  for  winding  and  general  dimen- 
sions: Speed,  2500  r.p.m.  on  125  cycles,  or  1200  r.p.m.  on  60  cycles.  Cast- 
iron  yoke,  laminated-iron  poles  cast  in.  Armature,  4  ins.  in  diameter,. 
3  ins.  long;  36  slots  3-16  in.  wide,  7-16  in.  deep,  every  sixth  slot  J  in.  deep; 
36  coils  of  No.  20  wire,  16  turns  per  coil,  4  wires  wide  and  4  deep.  Total, 
1152  conductors.  At  15  amperes  direct-current  output  the  cross-section 
of  armature  conductors  is  400  circ.  mils  per  ampere. 

Useful  lines  per  pole,  at  115  volts  and  2500  r.p.m.: 

1152  X  41.6 


115  X  ios 


=  240,000. 


TOTAL  LINES  PER  POLE,  320,000 


Part 

Total  lines 

Cross  sect, 
sq.  in. 

B. 

H. 

Length 

Ampere 
turns 

Armature  

I2O,OOO 

2. 

40,000 

10 

1-5* 

15 

2  air-gaps  

240,000 

4. 

60,000 

18,800 

.04 

75° 

5  teeth 

240  ooo 

2. 

I2O,OOO 

1  80 

•44 

70 

i  yoke 

1  60  ooo 

2  r 

46,000 

IO2 

•z. 

1  06 

2  cores 

3  2O,  OOO 

7.7C 

85  ,000 

18 

2.? 

4C 

Total  ampere  turns  in  field  winding,  995.     Circ.  mils  field  wire  (No. 

Mean  length   per  turn,    12   inches.     Turns 


11X12X500 
23)  =  -  r—  345 


i6X  12 

(approx.)  per  coil,  500;  16  layers  of  32  turns  each.  Resis.  of  field 
winding  (coils  in  series),  63  ohms.  Normal  shunt  current,  i  ampere 
(nearly).  Use  rheostat  of  about  40  ohms  total  in  field  circuit. 

Mean  length  of  wire  per  armature  coil,  16  feet.  Total  length  of 
armature  wire,  36  X  16  =  610  feet.  Total  weight  of  armature  wire,  2 
pounds.  Resistance  of  armature,  0.17  ohm.  Drop  in  armature  winding 
at  full  load,  2^  volts. 


CHAPTER  XXI 

FOUR-KILOWATT  COMBINED  ALTERNATING  AND  DIRECT-CURRENT 

MACHINE 

THE  machine  here  illustrated  is  the  largest  of  the  machines  of  the 
same  general  type  of  which  this  is  the  third  to  be  described  in  this  book. 
The  present  machine  has  8  poles;  its  speed  is  from  1800  to  1875  r.p.m., 
and  it  has  an  output  capacity  of  four  kilowatts. 

Fig.  205  shows  an  end  view  of  the  field,  base,  and  bearing  pedestals. 
The  field  has  a  circular  yoke  of  cast  iron  with  pole-pieces  of  laminated 
wrought  iron  cast  in.  About  No.  20  gage  iron  may  be  used  in  the  poles 
and  they  are  bored  out  to  5  9-16  ins.  diameter  after  being  cast  in.  Fig. 
206  is  a  section  of  the  assembled  machine,  which  shows  the  construction 
and  relation  of  the  various  parts.  The  armature  core  is  built  up  of  soft 
iron  discs  about  No.  27  gage,  having  an  external  diameter  of  5^  ins., 
with  a  2^-in.  hole  in  the  center.  The  discs  are  mounted  upon  three-arm 
spiders,  one  at  either  end  of  the  core,  and  the  arms  of  which  intermesh 
about  J  in.  at  the  center  of  the  core,  so  that  all  the  discs  are  supported  at 
least  three  points,  and  at  the  same  time  the  air  has  free  access  to  the  interior 
of  the  core.  Distance  pieces  are  provided  at  two  points  in  the  core  which 
divide  the  laminations  into  three  groups  with  3-i6-in.  ventilating  ducts 
between  them.  Two  hexagonal  nuts  upon  the  shaft  provide  means  for 
clamping  the  core  discs  and  spiders. 

The  commutator,  which  is  shown  partly  in  section,  is  3}  ins.  in  diameter 
and  if  ins.  wide  on  the  face.  There  are  48  segments  of  copper  with 
3j-in.  mica  between  them,  and  3-32-in.  insulation  separates  the  segments 
from  their  supporting  sleeve.  The  sleeve  is  of  machine  steel  and  has 
flanges  undercut  at  an  angle  of  60  degrees.  The  collector  rings  are  six  in 
number  and  are  made  of  copper.  The  rings  at  the  ends  are  f-in.  wide; 
the  rest  are  J  in.;  J-in.  insulation  separates  the  rings  from  each  other. 
The  bearings  have  a  brass  sleeve  fitting  the  shaft,  and  this  is  slotted  to 
allow  oil  rings  5-32  in.  wide  to  revolve  freely  with  the  shaft. 

Fig.  207  is  a  detail  of  the  armature  shaft.  This  is  designed  to  be  made 

169 


i  yo 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


from  a  piece  of  i  J-in.  cold-rolled  steel.  Threads  are  cut  at  both  ends  of  the 
core  portion  to  receive  the  hexagonal  nuts  which  compress  the  core  discs. 
At  the  alternating-current  end  of  the  machine  the  fly-wheel  pulley  is 
shown  in  position  upon  the  shaft.  A  pulley  of  this  kind  will  be  found  very 
useful  in  operating  the  machine  as  a  rotary  or  in  connection  with  a  gas 
engine  for  driving,  as  it  assists  the  armature  in  maintaining  a  uniform 
rate  of  rotation. 


FIG.  205 

Figs.  208  and  209  show  the  brush-holder  collars  or  so-called  "  quad- 
rants" for  the  alternating-current  and  direct-current  ends  of  the  machine. 
The  one  at  the  direct-current  end  has  eight  lugs  for  supporting  the  eight 
brush-holders,  and  the  alternating-current  end  has  six,  one  for  each  of  the 
six  rings.  Both  are  made  in  halves  and  screwed  together  after  being 
placed  in  position  on  the  bearings. 


FOUR-KILOWATT  COMBINED  ALTERNATING  MACHINE  171 


172 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


-H 


— Y?-~ 


FIG.  210 


FOUR-KILOWATT  COMBINED  ALTERNATING  MACHINE 


Fig.  210  shows  details  of  the  direct-current  and  alternating-current 
brush-holders.  The  direct-current  holders  are  for  radial  brushes,  f  in. 
thick,  ij  ins.  wide,  and  i  \  ins.  long,  and  are  provided  with  a  spring  tension 
arrangement,  the  details  of  which  are  shown  in  the  engraving.  The 
alternating-current  brush-holders  are  for  copper-leaf  brushes  J  in.  thick 
and  J  in.  wide;  the  spring  of  the  brush  itself  will  be  found  sufficient  to  give 
proper  contact  with  the  collector  rings.  The  studs  which  support  these 
holders  are  of  different  lengths  to  suit  the  position  of  the  various  collector 
rings.  The  dimension  marked  x  on  the  drawings  has  the  values  3!  ins., 
3^  ins.,  2\  ins.,  2  ins.,  if  ins.,  and  f  in.  for  the  six  studs  respectively. 
They  are  best  made  of  f-in.  brass  rod. 

Fig.  211  shows  an  end  view  of 
the  armature  core.  There  are  48 
slots,  3-16  in.  wide  and  J  in.  deep. 
If  these  slots  are  milled  out,  it  will 
be  necessary  to  take  the  discs  apart 
after  this  operation  in  order  to 


FIG.  211 


anneal  and  insulate  them  before  the  final  assembling.  Annealing  will  im- 
prove the  discs,  which  will  have  become  somewhat  hardened  from  the 
machine  work  which  has  been  done  upon  them. 

Figs.  212  and  213  show  developments  of  the  armature  winding.  This 
is  of  the  "straight-out"  type  and  is  of  two  forms,  known  as  the  "  short 
coil"  (Fig.  127),  and  "long  coil"  (Fig.  128).  The  long  coil  is  for  use  in  a 
four-pole  field  and  for  6o-cycle  work.  The  short  coil  is  for  eight  poles 
and  125  cycles.  These  coils  are  form  wound  of  No.  17  double-cotton- 
covered  wire,  12  turns  per  coil.  The  terminals  of  each  coil  are  brought 
out  at  its  apex,  and  are  connected  to  the  two  nearest  commutator  segments, 
inside  terminal  of  one  coil  and  the  outside  terminal  of  the  adjacent  coil 


174 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


FIG.  214 

connecting  to  the  same  segment.  This  will  bring  the 
neutral  point  or  line  of  commutation  at  or  near  the 
center  of  the  pole-pieces. 

Figs.  214  and  215  are  diagrams  to  guide  in  making 
taps  to  the  collector  rings.  The  eight-pole  arrange- 
ment is  intended  for  operating  on  i25-cycle  circuits, 
and  the  four-pole  for  6o-cycle  circuit.  The  necessary 


FIG.  215 


!____  3 ^ 


...I 


interconnections  between  segments  may  be  made  at  the  back  of  the  com- 
mutator before  it  is  placed  in  position  on  the  shaft.  For  instance,  in  the 
eight-pole  arrangement,  segments  i,  13,  25,  and  37  are  connected  together 


FOUR-KILOWATT  COMBINED  ALTERNATING  MACHINE 


and  to  a  lead  marked  No.  i.  The  leads 
numbered  i  to  6  inclusive  pass  through  the 
air  space  in  the  center  of  the  core  and  con- 
nect to  the  corresponding  rings.  Thus  con- 
nected, single-phase  current  may  be  obtained 
from  rings  1-2  or  3-4;  two-phase  currents 
from  1-2  and  3-4,  and  three-phase  currents 
from  1-5-6.  The  outputs  and  voltages  iire 
as  follows: 


Direct-current 

Single-phase  alternating . 
Two-phase  alternating.  . 
Three-phase  alternating . 


Amperes          Voltage 
35  "5 

35  80 

25  per  phase       80 
21  per  phase       70 


Figs.  216  and  217  show  the  details  of  the 


FIG.  21 j 

switch  cylinder  and  contacts  which  are  lo- 
cated in  the  base  of  the  machine  and  serve  as 
a  starting  device  for  operating  on  single- 
phase  circuits. 

A  strip  of  fiber  19  ins.  long,  i  in.  wide, 
and  |  in.  thick  is  fastened  to  the  under  side 
of  the  cast-iron  base  and  upon  this  are 
mounted  38  contact  springs,  each  f  in.  wide. 
The  cylinder  is  of  hard  wood  ij  ins.  in  di- 
ameter, and  is  of  the  proper  length  to  just 
go  inside  the  base  and  have  its  ends  jour- 
naled  therein.  The  free  ends  of  the  contact 
springs  press  upon  the  cylinder  and  make 
connections  with  the  contacts  fastened  upon 
the  cylinder,  but  they  can  only  be  in  con- 
nection with  one  row  at  a  time.  Fig.  217  is 
an  end  view  showing  details. 


v- 

0 
O 

<J 

3 

~y 

7 

fo 

o  O—  J 

E 

go^ 

Ja. 

tfO, 

z 

!°h 

~ 

2 

to- 

'oJ 

0 

"3 

o- 

3 

cx 
o- 

3 

o- 

3 

cx 
o- 

3 

CX 

o- 

3 

cx 

o- 

o- 

3 

cx 
o- 

3 

cx 
o- 

3 

cx 

0- 

3 

cx 
o 

3 

cx 
o 

3 

ex 
o- 

3 

cx 

0- 

o- 

—  ^ 

3 

Q 

176  DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 

The  diagram,  Fig.  218,  shows  how  the  connections  are  made  to  the 
switch  contacts.  The  uppermost  row  of  small  circles  indicates  the  contact 
springs  to  which  the  sectional  field  winding  is  connected.  There  are 
eight  coils  of  two  sections  each,  making  16  pairs  of  terminals  to  be  connected 
to  the  switch.  The  remaining  three  pairs  of  contacts  connect  with  the 
direct-current  brush  leads,  alternating-current  rings,  and  single-phase 
mains  in  the  manner  indicated.  The  lower  two  rows  of  circles  represent 
the  contact  pieces  upon-the  revolving  switch  cylinder,  these  being  simply 
connected  in  groups  by  means  of  short  wires  or  metal  strips  fastened  upon 
the  cylinder  itself  and  occupying  that  position  of  the  cylinder  over  which 
the  contact  springs  are  not  required  to  pass. 

The  action  of  this  device  may  readily  be  followed  by  assuming  that 
the  "starting"  row  of  contacts  has  been  moved  up  to  engage  the  contact 
springs,  when  it  will  be  seen  that  all  the  field  sections  are  in  multiple,  the 
armature  in  series  with  them,  and  the  whole  placed  across  the  single-phase 
alternating-current  mains,  so  that  the  machine  starts  as  a  series  motor. 
When  the  second  row  of  contacts  engages  the  contact  springs  the  field 
sections  will  be  in  series  and  placed  in  shunt  across  the  direct-current 
brushes,  while  at  the  same  time  the  single-phase  supply  current  is  connected 
to  the  collector  rings,  and  the  machine  is  now  operating  as  a  synchronous 
motor,  exciting  its  field  from  the  direct-current  end,  which  is  the  normal 
running  condition. 

To  operate  the  machine  at  no  volts  direct  current  or  i25-cycle  alter- 
nating current  no  changes  are  necessary  and  the  speed  will  be  1875  r.p.m. 
For  6o-cycle  alternating-current  work  the  number  of  poles  is  halved  by 
reversing  the  terminals  of  any  two  successive  field  coils,  skipping  the  two 
coils  and  reversing  the  next  two;  this  being  most  conveniently  done  by 
changing  the  connections  at  the  starting  switch.  This  change,  together 
with  the  "long  coil"  winding  and  the  diagram  of  connections  for  four 
poles,  fits  the  machine  for  operating  at  60  cycles.  The  speed  will  now  be 
1800  r.p.m.  and  the  voltage  and  output  practically  the  same  as  before. 

The  following  is  a  brief  summary  of  the  general  dimensions  and  data 
for  winding: 

Eight-pole  machine:  1800  r.p.m.  at  60  cycles;  1875  r.p.m.  at  125  cycles. 
Armature  5^  ins.  diameter,  4  ins.  long,  48  slots  3-16  in.  X  \  in.;  3-16  in. 
=  1 88  in.  width  of  slot,  allowing  three  No.  17  wires  and  insulation  of 
18  mils;  5  in.  depth  slot,  taking  eight  No.  17  wires  and  insulation  and 
bands  of  45  mils.,  giving  24  conductors  per  slot.  Total,  1,152  conductors. 
Direct-current  output  at  470  circ.  mils  per  ampere  =  36  amps. 

There  will  be  455  ampere-turns  in  each  field  coil.     Mean  length  of 

i  turn  =  13.5  inches  circ.  mils  shunt  wire  =  -  -  =;  465. 


FOUR-KILOWATT  COMBINED  ALTERNATING  MACHINE 


Use  No.  23,  having  509  circ.  mils,  .034  in.  diam.,  d.c.c.;  620  turns 
(approx.)  per  coil,  in  14  layers,  44  turns  wide.  Wind  in  two  sections  and 
bring  out  individual  terminals  from  each  section. 

8  X  620  X  13.5  X  20.3 
Resistance    of    shunt    field  =-  -=114  ohms. 


1000  X  12 


45° 


Normal    shunt    current  = -^-=  .75    amp.      Use    rheostat    of   about 


40  ohms  in  shunt  field.     Weight  of  wire  in  shunt  coils: 
8X620X13.5X1.54 

1000  X  12 

Total  length  of  wire  on  armature: 
48  X  i8X  12 


=  8.5  Ibs. 


12 


=  864  feet. 


Total  weight  of  wire  on  armature: 
864  X  6.2 


1000 


5.37  Ibs. 


Resistance  of  armature: 

1000  X  64 


=  .068  ohms. 


864  X  5.04 
Drop  in  armature  at  full  load: 

36  X  .068  =  2.45  volts. 


Part 

Material 

Total  lines 

Cross- 
section 

B. 

H. 

L 

Ampere 
turns 

i  armature  
2  air-gaps  
5  teeth  

Wrought  iron 
Air 
Wrought  iron 

170,000 
340,000 
340,000 

4.    in. 
6. 
2. 

42,500 
56,600 
113  ,OOO 

4 
17,880 
108 

i-S 

•031  3 
.e 

6 
566 

54 

2  cores  

Wrought  iron 

420,000 

c. 

85  ,OOO 

18 

1.7 

31 

i  yoke 

Cast  iron 

2IO  OOO 

47 

42  ooo 

68 

•7.7 

2S2 

Total  ampere-turns 909 


CHAPTER  XXII 
SINGLE-PHASE   RECTIFIER 

THE  accompanying  drawings  and  description  constitute  a  design  for 
a  machine  to  " rectify"  single-phase  alternating  current;  that  is,  to  change 
it  into  a  pulsating  direct-current  without  changing  its  e.m.f. 

Fig.  219  shows  an  end  view  of   the  field-magnet   with  two  coils  in 


i 


FIG.  219. 


place.  The  circular  yoke,  magnet  poles  and  feet  are  cast  in  one  piece, 
thus  avoiding  joints  in  the  magnetic  circuit  and  reducing  the  machine 
work  to  a  minimum.  The  pattern  for  the  field  casting  should  be  made 
in  two  pieces,  the  parting  being  made  along  the  line  A-B  in  Fig.  220. 

178 


SINGLE-PHASE  RECTIFIER 


179 


Fig.  221  shows  the  details  of  the  journal-box  bracket,  journal-box  and 
oil  ring.  The  bracket  is  bolted  to  machined  seats  on  the  field-magnet 
yoke  (see  Fig.  219).  The  difficulty  in  securing  proper  alignment  with 
this  construction  is  less  than  that  of  handling  and  machining  the  field 
magnet  when  journal  bracket  arms  are  cast  integral  with  it. 

Fig.  222  shows  a  section  through  the  armature,  commutator,  and 
collector  rings.  The  armature  core  is  built  up  of  laminated  iron  in  the 
usual  way,  and  held  together  by  heavy  washers  of  wrought  iron  threaded 
on  the  shaft  at  either  end.  A  cast-iron  core  may  be  used,  though  it  will, 
of  course,  heat  up  more  than  the  laminated  one. 

The  commutator  and  collector  rings  are  preferably  made  of  copper^ 


FIG.  220. 

through  brass  may  be  used.  A  piece  of  ingot  copper  can  be  obtained  and 
forged  into  a  circular  blank  suitable  for  turning  up  into  rings  and  a  com- 
mutator. The  commutator  is  turned  as  a  solid  cylinder  of  the  required 
section,  and  it  is  then  cut  into  four  equal  segments  with  a  milling  machine, 
or  with  a  sharp  hacksaw  and  hand  power,  if  a  milling  machine  is  not 
available.  The  segments  are  then  built  up  with  mica  insulation  and 
clamped  in  a  brass  sleeve"  fittirig~the  shaft. 

It  is  well  to  follow  the  design  of  arc  machine  commutators  to  some 
extent  and  to  allow  about  i-i6-in.  air  insulation  between  the  segments  at 
the  top.  Thus  the  mica  insulation  will  not  be  injured  if  sparking  occurs. 
Oil  and  copper  dust  should  not  be  allowed  to  accumulate  in  the  air  spaces, 
thus  formed,  as  this  would  cause  a  severe  short-circuit. 


i8o 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


Connections  are  made  between  the  collector  rings  and  commutator 
bars  with  some  strips  of  copper  about  1-32  in.  thick  and  f  in.  wide,  laid 
in  the  armature  slots,  which  have  been  made  about  1-16  in.  wider  than 
would  otherwise  be  necessary  in  order  to  accommodate  both  the  coils 


Sectiou  of  Bearing 
2  Wanted 


FlG.  221. 


FlG.   222. 


and  the  connection  strips.  The  back  collector  ring  is  drilled  with  J-  in. 
holes  at  four  equidistant  points;  two  of  these  holes,  the  opposite  ones,  go 
through  the  ring  and  part  way  into  the  front  ring,  the  other  two  holes  are 


SINGLE-PHASE  RECTIFIER 


181 


drilled  only  part  way  in.  Some  short  pieces  of  copper  wire,  about  No.  10, 
are  soldered  one  into  each  hole,  the  two  wires  from  the  front  ring  being 
insulated  from  the  other  ring  where  they  pass  through  it.  The  four  wires 
are  soldered  one  to  each  strip,  and  these  carry  the  current  across  the 
armature  and  connect  to  the  commutator  segments. 

Diametrically  opposite  segments  of  the  commutator  are  thus  connected 
to  the  same  collector  ring,  and  neighboring  segments  have  between  them 
the  whole  potential  difference  of  the  alternating  circuit.  It  is  much  better 
not  to  connect  the  copper  strips  permanently  to  the  commutator  until 
the  builder  has  decided  where  he  wishes  to  place  the  brushes ;  the  commu- 
tator may  then  be  twisted  around  on  the  shaft  to  the  correct  position  and 
the  connections  made  permanently.  The  brushes  may  be  placed  wherever 
they  will  be  most  convenient,  the  only  restriction  being  that  they  must 
be  90  degrees  apart  and  must  pass  from  one  segment  to  the  next  at  the 
same  instant  that  an  armature  tooth  is  exactly  under  a  pole. 


Armature  Coil  26  Wire  End  View  of  Core 

For  no  Volts 
4  Wanted 

FIG.  223. 

Fig.  223  shows  an  armature  coil  and  the  method  of  placing  the  coils 
upon  the  core.  The  coils  are  wound  on  a  form,  and,  after  being  taped, 
are  slipped  over  the  top  of  a  tooth.  The  slack  is  then  taken  up  by  bending 
the  ends  down  in  a  semicircular  shape  and  fastening  them  in  this  position 
by  screws  which  carry  small  fiber  or  hard  wood  bushings. 

In  addition  to  this  the  armature  should  be  banded  at  one  or  two  points 
with  No.  28  brass  or  German  silver  wire,  small  notches  having  been  turned 
in  the  core  to  receive  the  bands  and  allow  them  to  come  flush  with  the 
surface  of  the  core. 

With  an  iron-clad  armature  like  this,  the  clearance  need  not  be  more 
than  from  1-64  in.  to  1-32  in.;  just  how  much  it  will  be  depends  somewhat 
on  the  builder's  skill;  1-64  in.  clearance  has  been  indicated  on  the  drawings, 
and  with  care  taken  in  adjustment  it  should  not  be  difficult  to  obtain  this 
figure.  Fig.  224  shows  end  views  and  a  cross-section  of  the  rectifying 
commutator.  Fig.  225  is  a  fly-wheel  pulley  which  it  will  be  found  advis- 
able to  use  in  order  to  obtain  smooth  running. 


182 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


Fibre  Tube 


Fibre 


Mica 


Fig.  226  shows  the  brush-holder  yoke  and  brush-holders.  The 
bearings,  while  not  so  simple  in  construction  as  some  other  designs,  have 
proven  very  satisfactory.  The  rings  carry  up  a  plentiful  supply  of  oil, 

and  what  runs  out  at  the  end  returns  to  the 
well  and  does  not  fly  off  outside  the  bearing 
and  spatter  the  surroundings. 

In  finishing  the  bearings  the  bracket 
arms  are  preferably  faced  up  first.  The 
bracket  is  then  bolted  to  a  face-plate  and 
the  box  is  bored  out  to  a  diameter  of  f  in. 
clear  through.  Then  the  outside  of  the 
inner  boss  is  turned  off  ij  ins.  diameter 
where  it  is  to  receive  the  brush  yoke.  The 
sleeve  which  forms  the  bearing  proper  is 
turned  a  tight  fit  for  the  bore  of  the  box, 
so  that  with  but  little  pressure  from  the  cen- 
tering screw  it  is  held  firmly  in  place.  The 
grooves  for  oil  rings  can  be  cut  in  the 
sleeve  conveniently  by  mounting  it  eccen- 
trically in  the  chuck  and  using  a  thin  cut- 
off tool. 

The  brush  yoke  is  shown  with  two  arms 
90  degrees  apart.     Another  pair  of  arms 
and  brushes  might  be  added  if  it  is  de- 
sired to  have  more  current- carrying  capacity. 

The  direct-current  brushes  had  better  be  larger 
than  the  alternating- current  brushes,  and  the  holders 
should  have  spring  tension,  unless  a  very  springy  brush 
is  used.  Copper  brushes  are  better  for  this  purpose 
than  carbon,  as  they  make  better  contact  and  cause 
less  sparking. 

Figs.  227  and  228  show  the  field  and  armature  coils 
respectively,  with  the  forms  upon  which  they  are 
wound.  The  former  is  best  made  of  hard  wood,  and 
consists  of  a  block  and  two  flanges,  all  held  together 
by  two  wood  screws  and  having  a  J-in.  hole  through 
the  center  for  placing  on  a  mandrel  in  the  lathe.  The  FlG>  225> 

block  should  be  made  a  trifle  larger  than  the  pole 
over  which  the  finished  coil  is  intended  to  go,  and  it  should  be  given  a 
slight  taper  of  about  1-16  in.,  so  that  it  can  be  readily  slipped  out  of  the 
finished  coil. 

Before  beginning  the  winding  a  short  piece  of  tape  is  laid  in  the  long 


FIG.  224. 


T 


SINGLE-PHASE  RECTIFIER 


1*3 


sides  of  the  former,  with  the  ends  left  sticking  out.  When  the  form  is 
wound  full  these  pieces  of  tape  are  tied  tightly  over  the  coil,  and  will  hold 
it  in  shape  while  the  former  is  taken  apart  and  the  coil  is  receiving  its 


FiTore  Washer 

8 


2  Wanted 


FIG.  226. 


wrapping  of  tape.  After  being  shellacked  and  dried,  the  coil  is  placed 
on  the  poles  and  hard  wood  wedges  driven  in  between  coil  and  pole,  thus 
holding  it  securely  in  place. 


* 


Ft  tup  BOBBIN. 

WIN&  UP  TO  sat 
WITH  *20  O.CC.  w 


FIGS.  227  AND  228. 


The  same  form  may  be  made  to  serve  for  both  field  and  armature 
coils,  if  the  field  coils  are  wound  first,  and  then  the  block  reduced  in  thick- 


1 84 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


ness  from  f  in.  to  f  in.,  the  armature  coils  having  the  same  inside  dimensions 
as  the  field  coils,  but  being  only  half  as  thick. 

The  fields  are  wound  with  No.  28  double-cotton-covered  wire  and  the 
armature  with  No.  23.  If  the  coils  are  wound  to  the  specified  dimensions 
they  will  have  nearly  enough  the  required  number  of  turns. 

Fig.  229  shows  a  diagram  of  connections  and  Fig.  230  some  e.m.f. 
curves.  For  100  volts  the  field  and  armature  coils  are  connected  four  in 
series,  as  shown.  For  50  volts  the  coils  may  be  connected  two  in  series 
and  the  twos  in  multiple.  The  armature  terminals  are  tapped  onto  the 


FIGS.  229  AND  230. 

collector  rings,  or  what  amounts  to  the  same  thing,  placed  across  any  two 
successive  commutator  segments. 

The  connections  on  both  armature  and  field  should  be  such  as  to  pro- 
duce alternate  north  and  south  polarity  all  the  way  round.  If  all  the  coils 
have  been  wound  in  the  same  direction  and  placed  on  the  poles  the  same 
way,  connect  beginning  to  beginning  and  ending  to  ending,  and  the  polarity 
will  be  right.  The  machine  will  run  at  1800  r.p.m.  on  a  6o-cycle  circuit, 
and  on  a  i25~cycle  circuit  it  will  have  to  make  3750  r.p.m.  This  it  can 
easily  do  if  the  armature  is  as  well  balanced  as  it  should  be. 

Since  the  strength  of  the  field  has  a  considerable  effect  on  the  behavior 
of  a  synchronous  motor,  it  is  best  to  have  an  adjustable  resistance  in  the 


SINGLE-PHASE  RECTIFIER  185 

field  circuit  of  this  machine,  so  that  the  field  can  be  adjusted  until  the 
minimum  armature  current  is  obtained. 

Referring  now  to  the  curves  in  Fig.  230,  it  is  clear  that  if  the  rectifier 
is  running  in  synchronism  and  the  angular  position  of  the  brushes  is  correct, 
the  brushes  will  pass  from  segment  to  segment  at  the  instant  when  the 
e.m,f.  curve  reaches  its  zero  value  at  the  points,  a,  a,  a,  etc.  As  the  brushes 
in  passing  from  segment  to  segment  overlap  two  segments  for  a  brief 
interval,  they  form  a  dead  short-circuit  on  the  alternating-current  mains 
during  the  interval.  This  will  not,  however,  result  in  any  damage  if  the 
e.m.f.  becomes  zero  at  the  same  instance.  If,  however,  the  brushes  had 
been  incorrectly  placed  and  commutation  occurred  at  the  points,  6,  6,  6, 
etc.,  an  e.m.f.  of  value  equal  to  the  ordinate  at  b  would  be  short-circuited 
four  times  in  a  revolution,  and  serious  sparking  would  result. 

This  state  of  affairs  is  easily  remedied  by  shifting  the  brushes,  which 
corresponds  to  changing  the  angular  position  of  the  point  of  commutation, 
until  a  position  such  as  a  a  is  reached,  when  all  sparking  will  disappear. 
If  the  armature  falls  out  of  step,  or  if  it  is  thrown  into  circuit  before  com- 
plete synchronism  is  reached,  a  short-circuit  travels  over  every  portion  of 
the  e.m.f.  wave,  at  a  slow  rate  equal  to  the  difference  between  synchronous 
speed  and  the  actual  speed  at  that  instant,  the  result  being  a  magnificent 
display  of  fireworks  and  probably  a  blown  fuse. 

To  obviate  this  latter  difficulty  a  resistance  or  choking  coil  should  be 
placed  in  series  with  the  alternating-current  end  at  the  moment  of  starting, 
and  cut  out  when  it  is  seen  that  the  machine  has  settled  down  to  steady 
running.  Such  a  resistance  will  not  have  any  appreciable  effect  on  the 
small  current  drawn  by  the  armature  and  field  windings,  but  should  be 
of  such  a  value  as  to  limit  the  current  to  about  10  amperes,  should  a  short- 
circuit  occur. 

The  ordinary  method  of  using  a  synchronizing  lamp  is  not  easily 
applicable  here  on  account  of  the  small  size  of  the  machine;  and,  more- 
over, a  little  practice  will  enable  the  operator  to  judge  by  ear  the  proper 
instant  for  closing  the  circuit. 

By  making  slight  changes  in  the  connections,  as  already  pointed  out, 
this  machine  may  be  used  as  a  rectifier  on  single-phase  circuits  of  50  or 
100  volts  and  60  or  125  cycles.  The  amount  of  rectified  current  which 
may  be  drawn  is  not  limited  in  any  way  by  the  horse-power  capacity,  but 
will  generally  be  limited  only  by  the  capacity  of  the  transformer  which  is 
supplying  the  current  and  by  the  current-carrying  capacity  of  the  brushes 
and  other  parts  of  the  main  circuit.  Thus  from  50  to  100  amperes  may 
be  drawn,  depending  somewhat  on  the  nature  of  the  load  into  which  the 
rectifier  is  feeding  current. 

The  machine  may  also  be  used  as  a  self-exciting  synchronous  motor, 


i86 


DESIGNS  FOR  SMALL  DYNAMOS  AND  MOTORS 


developing  from  i-io  to  J  horse-power,  according  to  the  strength  of  field; 
and  finally  it  may  be  driven  by  belt  as  a  self-exciting  alternator,  supplying 


FIG.  231. 

either  an  alternating  current  or  a  rectified  direct  current,  or  both,  up  to 
about  100  watts  output. 

Fig.  231  was  reproduced  from  a  photograph  illustrating  a  rectifier  built 
from  this  design  by  Parsell  &  Weed,  New  York. 


APR  1 3  194' 


YC  33520 


789547 


Engineering 
Library 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


m 


